05,
I don't have any first hand knowledge, nor do I have completely accurate numbers. But I think the size of baseball teams, the high number of D1 teams (almost 300), and the MLB draft process make being in the Top 1000 pretty special.
In basketball we think of the top 150 as elite and the top 300 as very good. In football it is the top 250 and there are 372 4 and 5 star players in the Rivals database. Plus we know that at least double that (3 star players) are very talented.
Why should baseball be 3x those sports?
When you look at the number of D1 teams by sport:
Basketball ~350
Baseball ~300
Football ~ 125
The number of player on each team:
Basketball ~13
Baseball ~35
Football ~ 85
Those things probably make them prett similar but when you factor in the MLB draft process that changes things. I don't know the real numbers but I'm guessing that a couple hundred or even more HS players sign pro contracts each year.
Finally the pro draft process.:
Basketball - no HS players drafted
Football - no HS players drafted and most players stay 4-5 years even elite players
Baseball - over 1200 draft picks a year, at least half are HS players and probably 1/2 or more sign with MLB teams.