That is an excellent point. However, I struggle getting past the notion that the odds of success are far greater with a top 100 recruit than they are without a top 100 recruit. It's probably best to consider a variety of inputs regarding players, such as their ranking, their level of competition, potential baggage, and fit, instead of just looking at ranking.
Couple of things:
I think one thing we all have to remember when we think of the "Top 100 Kids" is that while the RSCI is an average of their ratings, there's so many differing opinions on how to rank a player that sometimes a consensus actually hasn't been reached. All of the rankings have their own little idiosyncrasies in how they do their rankings. Some are ranking players based upon who they feel are the best high school players. Others do it on who they feel are the most college ready. Others on who are the most NBA ready. Others on who has the most potential to be a great college player. Others on who has the most subjective talent. So while they all number people from 1-100, the numbers mean different things to different people. That's why you see guys like Nick Williams ranked #35 by one expert and not in the top 100 of others. There is no set standard for how they do their evaluations.
There's also a lot of politics involved. Going back to Nick Williams, one of the reasons he was ranked #35 by ESPN, was that ESPN's ranking back then was done by Bob Gibbons. Williams had played in Gibbons' Tournament of Champions AAU event, and played well. When it comes time for him to do the rankings, Gibbons is known for unnaturally favoring player who played and played well in his event, even if they were not able to repeat that performance in other events. Dave Telep on the other hand looks not only at how the guys are playing but outside factors like attitude, academics, surroundings etc. Each of the services have their own little things they look at that effects an impartial evaluation.
Given that, I've never been particularly comfortable with labeling a kid as a top 100 player, since there are so many different things that go into that sort of ranking. On to your points:
Looking at a few other numbers, it makes it easier to see why a high percentage of Top 100 players are not significant contributors. In the RSCI top 100 from 2008 and 2007, I counted 93 players and 95 players that went to BCS conference schools, respectively. In other words, almost all of the top 100 players go to BCS schools. Add Memphis into the mix and the percentages go even higher.
Yes and no. Just looking at the 2006 names I mentioned, most of the reasons for disappointment were their own and not caused by another player:
Vernon Macklin - he was the back up to Hibbert, who was not a top 100 player before transferring and word out of UF is he's still not ready to contribute
Derrick Caracter - character issues kept him from reaching his supposed potential. Moments of greatness, but he's a headcase.
Lance Thomas - he's surrounded by talented players, but even when given significant minutes he doesn't produce, and he's turned out not to be the athlete people thought he was.
Brian Zoubek - he's been given every opportunity to show he deserved the ranking. But he's never been able to develop on the court even when given significant playing time
Ramar Smith - attitude issues caused his demise, he could never get out of his own way
Duke Crews - see Ramar Smith
Curtis Kelly - he had a logjam in front of him with Robinson and Adrien.
Willie Kemp - admittedly had talent in front of him, but even when Memphis was struggling for a true PG before Rose, he couldn't get it done
James Keefe - can't guard anyone to save his life
Mike Jones - didn't even make it into school and has now been dismissed from two schools for attitude problems
Brian Carlwell - was behind top 100 player Shaun Pruitt, but even as a backup didn't contribute before getting hurt and transferring
Tom Herzog - even after a redshirt year, he wasn't ready for Big 10 ball. MSU goes small rather than play him
Jamie Skeen - got injured, then got fat, then decided he was best suited as a bad shooting perimeter center and ended up transferring
Jonathan Kreft -couldn't even make it on campus before getting arrested for drug possession
Doug Wiggins - headcase. Backup behind top guys at UConn, but even after a transfer and a chance to show his talent, he got arrested for B&E and might have been expelled from UMass.
Perry Stevenson - starter this year, playing almost 30MPG. Never bulked up or added post moves to make himself a legit SEC player.
Edgar Sosa - UL doesn't have another top 100 player at the PG position, but Sosa was relegated to bench duty after he couldn't beat out Andre McGee. Has never been able to understand Pitino's system, or cut down on mistakes, or any thing you need a PG to do.
Anthony Gurley - given plenty of time, and played well on occasion but showed no consistency. Transferred after Skip Prosser died and was okay at UMass, but a top 60 prospect should be more than ok.
Jamil Tucker - as a 6'9 240lb center, he spends more time beyond the arc than in the post despite actual post talent.
Isaih Dahlman - given every opportunity to prove himself, he's been unable to beat out anyone or even earn significant minutes
Keith Clark - got injured as a freshman, and averaged 5PPG as the back up to the Griffin brothers. Stupidly declared for NBA, now in NBA DL.
Nigel Munson - couldn't get along with Seth Greenberg even though he would have had a chance to start as a sophomore. Left school for a JUCO, never enrolled, nowhere to be found, may have given up the game.
Phil Nelson - started 9 games and played in every game...but not well. Transferred to Portland State where he's been okay but you would expect more from #71 at that level.
Pierre Niles - weight problems and inability to play Memphis fast paced offense keep him off the court.
Mamadou Diarra - couldn't even contribute as a back up. Yes USC has talent in front of him, but he can't even get 5 minutes a game.
Antonio Pena - starts, but doesn't contribute much. Can't beat out Shane Clark a non top 100 player
Leon Freeman - still has not enrolled at a school because of academic issues
William Graves - already mentioned. Players ahead of him sure, but he also got suspended
Josue Soto - couldn't beat out the other disappoint top 100 players at FSU, now at Florida International
Donneal Mack - talented players ahead of him, that I'll give you. Tried to transfer then came back.
Jonathan Mitchell - he couldn't beat out the other top 100 players to start and didn't really contribute off the bench. We'll see how he does at Rutgers now.
Taylor Harrison - barely got off the bench, got hurt at the end of his freshman year, hasn't played since
Soloman Tat - behind Sean Singletery as a freshman, he was expected to start after that since UVA desperate for talent, he played less than 10MPG in a total of 17 games this year and scored 11 total points.
Dan Werner - starter as a junior, averaged less than 9PPG.
Jeremy Mayfield - given a chance for big minutes, he couldn't do anything with them. Less than 5PPG before becoming academically ineligible
Cameron Tatum - stuck behind a lot of talent, that one I'll give you.
Daniel Deane - couldn't hack it at Utah with not much talent around him. Now at Oregon State where he is slightly improved...but that doesn't say much.
Hamady N'Diaye - RU is desperate for a big man, and he's got over 20 minutes a game for two years. Can't stay out of foul trouble, can't really score either.
Adrian Graves - lots of talent around him at Xavier, but he couldn't contribute at all off the bench. Got kicked out of school now at Bowling Green
Now I'm coming full circle, however. If so many of the top 100 kids are entering BCS programs every year, how does a program compete if it is not signing them on a regular basis?
How did MU compete in the toughest conference in the country with only three true top 100 players? You don't need to bring in a boatload of top 100 kids every year to be successful, but you need to hit on the ones you bring in. You also need to have a fairly well developed scouting system and a good on the court system so you can identify players that may fit the role you need that aren't top 100 types. And you need to be very good at player development when you get guys that are raw.
Maybe most importantly, you need to recruit good kids. I think a lot of the services get caught up in looking at the player's physical attributes and skillset and don't look enough at attitude and things like desire and will to win. If you can get a guy that wants to work hard every day, wants to get better every day, and is coachable...you can turn him into a player regardless of where he was out of high school.