A) I thought you were graded on how many anweres were correct, not wrong
B) I'm pretty sure you're only scored against people with the same form. Otherwise, it doesn't seem to be very standardized.
C) You're expected to know everything, but that isn't really possible. A little luck comes into play to get a really high score, such as receiving a form that is composed mostly of stuff you know well and are pretty good at. But, ultimately it is up to YOU to study what needs to be studied.
My lowest section is PS. I can bring it up. I know physics very well now, it's my highest GPA. (3.68 for physics and genchem). However, I made two mistakes. The first time I took the MCAT, I had not had Physics II. I didn't really put much study time into optics and E&M and learning all the formulae. My form was mostly E&M.
The second time, after having physics II, I reviewed and pimped myself on E&M and knew it inside out. I spent about two straight weeks on nothing but physics. I neglected gen chem, which by that time was a class I took 3 years ago. My form was mostly genchem with some E&M stuff thrown in, and naturally I couldn't remember **** from genchem. My score went up, but not as much as it should have.
I now know that anything is fair game because of the variation of forms and administrations. If, for some reason, I decide to retake the MCAT, I'm spending weeks on PS alone.
The only plus side is that I'm flying through astrophysics and astronomy because I know physics so well. At least something came out of it.