I think you're on to something here. Most people don't know what it's like to really be part of a passionate fanbase. Sure, you can be a diehard fan of your local professional sports team, but what connection do you really have? You live in the same city or state, therefore you're a fan. But you still really have no real connection. With a school, you are part of that institution. While you're not part of the team, there's definitely more connection to it. When somebody says something bad about it, you take it a bit more personally.
Seems like Sioux fans foster that type of intensity and it doesn't seem to exist at most schools. Once a Sioux fan, always a Sioux fan. But with a lot of schools, it seems to me, once you leave the school, the fans couldn't care less what's going on there.