The way I see it, there are thousands of people who are both brilliantly qualified to attend medical school and want to attend for the right reasons.
Unfortunately, the amount of spots (as we all well know) available is far less than the number of qualified people.
Therefore, if a medical school wants the most talented/best fitting class for the school, they will scrutinize the applications/recommendations before making the final cut...
So, let's say that admissions committee member Dr. Smith is reading over Candidate Z's file. Dr. Smith notices that her good friend Dr. Jones (who is also a professor at the same medical school) wrote Candidate Z is superb recommendation. Dr. Jones has a great reputation as well. Since Dr. Jones is both a good friend of Dr. Smith and willing to stake his reputation on someone, Candidate Z is given a letter of acceptance.
(We all know there is a little more to this in terms of academics and extracurriculars and MCATs, but you get the idea.)
Alternatively, if Dr. Smith hated Dr. Jones or if Dr. Jones had a horrible reputation, this could be much different scenario.
Med school admissions are so competitive that it seems that things like this push people into the "Accepted" category...
Maybe I am way off on this, but this seems to be completely possible.