Some medical schools, like GW for example, get 11,000 applications per year. They don't have the staff or inclination to parse through transcripts to see who took calculus based physics and who didn't. They have no way of comparing a transcript from Carleton with a transcript from Mankato other than taking them at face value. Furthermore, there is no study which shows, after controlling for SAT/ACT scores of undergraduate freshmen, that more rigorous schools produce higher MCAT scores.
I'm sorry but if you don't have the numbers you aren't going to get into a US MD school. It's that simple. Even applicants with screaming MCAT scores experience a precipitous decline in the probability of acceptance with lower GPAs. Stare at the data:
The fact is weaker competition gives a serious applicant more time to add the intangible fluff to his/her application. Hand out cookies at the local ER? Check. Wash out test tubes and get coffee for some Prima Donna researcher? All over it.