It sure is a mystery. I've received exactly one fee waiver from Illinois (where I'm living now), and none from Oklahoma (I went to OU), but a bunch from all over the East coast.
I have two friends who both went to better UG schools than mine, and both scored significantly better than I did on the LSAT (168 and 172), and they said they got 3 or 4 fee waivers each.
I guess I'll just sit back and keep enjoying the flood of mail. It makes me feel popular.
As a thought, would being kinda older (I'm 26, graduated in December of 2000) make me more likely to get fee waivers? Do they even know that from the information they get from CRS?