You really have the question backwards. You can do well on the MCAT having taken the prerequisite classes, and not going through review material (e.g. Kaplan, Princeton Review). Of course, if you slack off during classes, it'll reflect on your MCAT score. The problem with trying to learn everything from review books is that they leave out a lot of the finer points, which reinforce concepts. And then, you also have to look at it on a class-by-class basis. Physics and bio you can teach yourself pretty easily. Chemistry, on the other hand, lab helps quite a lot. You can "read" about TLC & spectroscopy, but it makes a whole lot more sense if you actually do the experiments. The same can be said about gravimetric analysis, titrations, etc. I haven't done O-Chem yet, but I imagine its the same situation. As for Kaplan/Princeton Review, these are what the name says - review courses. You be the judge: could you pass the bio final at your uni, if your only knowledge is from a review book? My guess is that these review courses have a certain expectation when you take them, e.g. you can differentiate between a solar cell, prison cell, and living cell. And that your knowledge of living cells goes beyond "uh, it can cause cancer man, if it spreads like crazy." They would expect you to have been exposed to mitosis, meiosis, the electron transport chain, Krebs Cycle, cell cycle, the cytoskeleton, cell structure, DNA, RNA, basic Mendelian genetics, etc. And I would guess, if your intention was to go to med school, it would be helpful to know about specialized cells, e.g. neuron, cardiac muscle cells, hepatocytes, epithelial cells, etc: where these can be found, their function, turnover rate, etc. Review books can't go into detail about these things, or they'd turn into textbooks. So in the final analysis, you're better off taking the classes. Review books will help you organize your thoughts, with a specific emphasis on the MCAT. This is good, given the sheer volume of info you're expected to deal with.
