Seems to me (I could be way off here), that during the MLB draft every summer, you hear something along the lines of "John Smith committed to play at Virginia Tech, but has decided to accept the contract offered by X team".
How do the college teams manage their rosters? Over-recruit, assuming you will lose 1 or 2? Do the coaches have a "feel" for who committed but probably won't make it to campus? I'd imagine they'd have a better handle on 3rd years, since they've seen their progression and hear the chatter.