Umm, midweek is defined as football on Monday, Tuesday, Wednesday nights. Friday night is the start of the weekend for most Americans. For many others the start is Thursday and plenty of people if they don't have Friday off are willing to take a vacation day once a year to travel in for a football game. Almost all of the conferences have some Thursday and Friday games. The MAC is will put a game like Buffalo vs. Ohio on a Tuesday that isn't a big game to begin with and attendance plummets.
I agree with some of this. Certainly Monday through Wednesday is different than Thursday and especially Friday. Of course, Friday is high school football night, so that is something that can detract from attendance some,but a school like USC probably would sell out for a game at 3 a.m. in the middle of the week.
From what I can remember, with the exception of the first Thursday of the season and holidays, the Big 10 and SEC don't play weekday games. I think the Big 12 and now the Pac 10 just recently started playing a few. It's a new trend for TV and money that comes with it.
I still don't think games being on Tuesday and Wednesday nights in MAC play causes attendance to "plummet." It seems to drop slightly compared to other games in November when attendance already is dropping anyway.