Oh definitely. As drizzt shows below, some people can accomplish great things with less time invested. That's obviously the exception to the rule, so it's best to realize (as early on as possible) what kind of effort you're willing to put in, and what kind of results that gets you.
I never took any sort of biochemistry or genetics or microbio courses, which made me feel like a stranger in a strange land during much of M1. We actually started M1 with anatomy (like most schools), and I fortunately had taken a human anatomy course in undergrad, so at least that wasn't foreign to me, and although I got the highest score in my class for the course, I probably put in less time than about half of them. The rest of the year, however, was filled with transient feelings of inadequacy as we dealt with plenty of topics in cell/molecular bio or physiology that I had either never seen/heard of, or had completely forgotten because it had been so long since I was exposed (I'm a non-trad student). Anyway, the success I found during Anatomy (for which I am grateful) sort of lit the fire under my ass and made me realize that it was possible to "ace" courses in med school; however, at the time my thinking was that the only reason I did so in Anatomy was because I had seen a lot of it before, which led to a "fear" that drove me to working those crazy hours referenced above in order to try to stay on top.
As many will probably agree, the law of diminishing returns comes into play here quite a bit. I am sure that I (and most) students could've passed the classes just fine with noticeably fewer hours of studying per week. But I guess I figured those extra couple points on each test were worth it to me. I will also conceded that M1/M2 were not the most thrilling/exciting/joyful years of my life as a result of all the work I put in, but now that I'm on the other side of the fence, I'm glad I did it.