Also, considering that the average price for a rush ticket is around 25 bucks or so, it's not like those tickets are going to be a big money maker for the producers.
I can see why they do a student rush over a general one. If you look at some shows there have been cases where the people sitting in line get too out of hand and the producers might now wish to deal with that. Therefor, they might do a student rush to mitigate that problem.
"If you try to shag my husband while I am still alive, I will shove the art of motorcycle maintenance up your rancid little Cu**. That's a good dear"
Tom Stoppard's Rock N Roll