I assure you that 99.9% of us (short of you, a few others on this thread, and maybe Will Hunting) if given a physics book, an ochem book, and a bio book, and told we had 4 months to learn the material on our own would not be able to learn it. One, because people need structure -- weekly assignments, tests, and class time. Two, and equally as important, testbooks aren't 100% clear, and that is why we have professors and TAs, to explain the material and help us work through problems.
I think that besides educating you on subjects you choose (i.e. your major), the point of college is also to teach you how to think on your own. Let's face it -- there's no career where you get paid to read a book and memorize all the ideas in it. Whether you go into medicine, research, sociology, whatever -- you need to be able to think. And at least 75% of all the professors I've had at college have had that philosopy, and made it clear that they DON'T want us to simply memorize the text.
Anyways, that's just my $.02.