don't worry about it. some firms (like mine) prefer to interview all the candidates from a particular school before they decide who from that school gets an offer. maybe you had some late callbacks from your school. or maybe someone else declined. whatever...doesn't matter.
and BTW...it only SEEMS like they're going to make you "rich." it's not as much money as it seems at this point. know what you're going to do with that money before you start, and stick to that plan. it's a lot of money/week, but there aren't that many weeks, esp if (like i did) you have bills backing up before that first paycheck.