Interesting. In my social circle we have a longstanding tradition of organizing our biggest events for Tuesdays - and we aren't alone. Go to a "normal" bar on a Tuesday night, and they'll probably close at 11PM and the only people there are a few drunken bums. Go to a student bar, on the other hand, and there's a respectable turnout - but mostly of older students. Seniors and graduates mostly. The Just-21 crowd will be conspicuously absent.
I think there's just some sort of draw towards Tuesday nights being a sort of counterculture late-collegiate powerhouse - it stands in stark contrast to the freshman-heavy weekends, and is strategically located so that you've (maybe) been to all your classes once that week, and as such know just how fucked you are and need to unwind.