DG,
This goes back to what it takes for success vs. what it takes to get an opportunity. You'll see a lot of pitchers at the AAA level in pro ball throwing in the mid eighties. I'm guessing that almost every one of them was able to throw high eighties or low 90s when they were drafted. Pitchers are going to have more success at the higher levels locating in the mid 80s than they are just getting the ball over at 90.
Pros and college both want kids who can throw hard because they can still have decent velocity once they teach them to back off and pitch rather than just throw hard. Remember, as good as Maddux is now he was much better when he threw a bit harder and he was able to throw low 90s out of HS.