Laptop Usage Elsewhere
Chances are you will actually find the portability of a laptop to be more convenient for things that you do outside of the classroom. Here are a couple of examples to consider:
Your roommate doesn't have homework today but you do. Thus, he is having a party. As much as you'd like to join right in and party it up, you have assignments due at 8:00AM tomorrow morning. With a laptop, you can go to the library, find a room and study (without the distractions), or go to a buddy's place and study.
You are struggling badly with a take home test, spending 20 minutes on each question. For this, it can be of great benefit to study with someone that's in your class, and work on the test together. For stuff like this, it's always nice to have a laptop, so that you can work at their place, or yours, and work on the test at the same time.
Your stupid printer is not working and you need to print 10 pages before class starts in an hour. Carrying your laptop to a working printer is much easier than finding a working printer and carrying it to a desktop PC. Of course, flash drives also work great for stuff like this; but what are you going to do when you get to the library to print the paper, and there is not an open computer in sight?
In college, time is usually difficult to manage. If you want to go to the beer pong party tonight, you need to eat some dinner, do laundry, and get some homework done before you go. With a laptop you can pickup McDonalds, eat while your on your way to the laundromat, get your clothes started, and type the report while they are washing.