I work at a university and while I don't spend much time in computer labs these days, I do recall being in a Mac lab a year or two ago. It was filled with a bunch of pissed off students who had an assignment that involved using software only available on Macs. No one could figure out how to use them. They looked at me and I told them I couldn't help and got out of there before things turned ugly. It's more than just cost, it's also what people know how to use. If you're in college time is important and learning a new OS isn't what people want to do, they just want to do their assignments.