I think it also depends on your undergraduate institution. If you went to a well-known, well respected UG, your MCAT may be less important, but if you went to a no-name state school (like I did) then supposedly they give greater weight to your MCAT. I have read that the reason they do this because the MCAT is supposed to be a standardized assessment of your knowledge/critical thinking skills, whereas grades could differ from school to school (because of grade inflation, course difficulty, etc.)