I don't know where most of the posters in this thread go to school, but I think college style depends on the type of campus you attend, what you're going to do there, and the overall weather of where you live.
My campus covers about 18,000 square feet. Sometimes, I only have 10 minutes to rush from one end of the campus to the other to get to my next class. Oh, and did I mention some genius decided to build our campus on a hill? I also walk to class from home instead of taking the bus/driving. There is no way I am wearing heels because my feet would be dead by the end of the day. I'd rather wear sneakers or something else that is comfortable.
I'm also a science student, which means I constantly have labs. Although I do wear a lab coat and take safety precautions, there are times when chemicals I am using spill onto my shoes and lower legs. As a result, we're required to wear pants and closed shoes (ie. no flats, peep toes, flip flops) whenever we have a lab. Even if we weren't, I wouldn't wear a dress or nice pants anyway because I don't want acid ruining them. So a lot of times, people wear sweatpants because it doesn't matter if something spills on them. As for shoes, you're not allowed to sit down (because you won't be keeping an eye on your experiment) and the labs last 3 hours. Comfortable footwear is key in this situation.
Lastly, my college is in the snowbelt region of Ontario. Although I would love to wear nice (and usually expensive) boots here, it snows constantly and the salt used to melt the snow destroys the material. You need something that is warm (Uggs) and built to last (winter boots, ie. Sorel). It is also extremely cold - our average winter temperature is about -6.7 Celsius or 20 Fahrenheit. On the really cold days (which is most of December - February), it really helps to wear tights underneath sweatpants as an extra layer of warmth (and usually, only sweatpants provide enough room to fit them).
I don't mean to make it sound like some people have no choice but to wear frumpy clothes to school, but in some situations, it's the best (practical) choice. Sometimes, it's better to be practical over fashionable. Of course, this doesn't excuse the people who don't brush their hair or attempt to be hygienic.
That said, I don't own Uggs or sweatpants myself (I prefer form-fitting yoga pants) but they are really popular on my campus and it's not hard to see why.