<p>Many students study for a few months, take the MCAT, realize that their scores are not high enough, and don't bother applying. Admit rates at some schools are as low as 3%. It's the total number of doctors that is the problem, though. There are not enough, and that is why we consistently import doctors from abroad. Unfortunately, many come here for medical school and then leave, worsening the shortage. Current doctors are happy with the resulting supply and demand, since a shortage allows them to still charge enough, despite the discounts they are taking by hooking up with HMOs.
It's true that some Ph.D's can take a long time, as some can take a short time. Obviously, an M.D.'s length of training will depend on the specialty. On average, however, it's longer and more arduous than a Ph.D. Radiology=13 years total (well, 17 if you count college). But doing research and writing for a number of years is a different experience from being slave labor in a hospital and not sleeping for 3 days at the drop of a hat.</p>