The problem with sitting in the student section without a student ticket, is there are 2500 seats for students and 3500 tickets sold. (I think that is still the number, by ivam basing it off of last year) The students are already out of room for big games like Michigan, Kansas or even Iowa.
(Of course, I have student tickets, but I don't always sit in the student section...and have had friends without student tickets sit with me in the student section, so I am being a complete hypocrite here.)
In regards to the entry policy for students, the students lost the privledge to all cram into the stairs last year against Kansas. They broke some doors, ran past ticketers without being scanned, and caused other problems when the doors open (and before the doors open, like lighting a Kansas fan's hat on fire, in the middle of a large crowd of people.) And the single file line is the fairer method anyways.