Of course those combined med students are just as capable, but perhaps their drive/motivation is not as forthcoming; they're basically guaranteed entry by merely maintaining a credit (although it's fair to say they would be aiming higher, but there's no real sense of competition). In Med Sci, you start out with at about 150 people trying for dear life to make it into the top 15 - when you have such a competitive environment with extremely competent students, obviously marks will be skewered, particularly in the first year.