Just fyi - the difference in weight between the macbook and 15" macbook pro is about 6 ounces. The MBP offers a bigger screen and better speakers, and other than that you will not notice a difference in the performance for anything you'd be doing related to law school.
If you're into audio/video editing, 3d rendering, or gaming, then the MBP would be a much better choice.
The plastic macbook scratches easily, the aluminum macbook pro dents easily. There are plenty of cases, guards and shells available for both, though.