have heard from a few current students about this and here are the two main schools of thought
1) I'll get what i like: Well most of the times the laptops offered by the schools are non-configurable and over-priced. And if i already have one then why not keep using it. (and save some $$$) And i can fix any s/w or small h/w glitches myself, if the need be
2) I'll let school worry about the machine. what if your laptop flipped during exam period. Most of the schools have a tech team which will only support laptops bought through the school's laptop program. they might quickly fix/replace your laptop if it crashes in dire situations.
So, i believe it's like buying an insurance
....i am not going to get hit by a car vs. what if i do?
personally, i fall in category 1.