My first thought was the same as MilkmanAl's. It seems like the vast majority of people in my biochemistry class (for majors) are pre-medical, but I can tell you that many of them are not even doing great in this class and are certainly not prepared for medical school. Nonetheless, some of them have probably always wanted to be a doctor, and so they will apply anyway, and some of them will get denied.
If you're a music major who is deciding to apply to medical school it seems much more likely that you're doing so because you're very qualified and, as Narmer pointed out, you're already ahead of many clueless pre-meds in your understanding that majoring in a science is unnecessary.
There may be some actual causation too, don't get me wrong. Being well rounded is good, and having a major that clearly reflects that is probably helpful.
I'm not sure who thinks that biochemistry would be an easier path to medical school. As
LizzyM mentioned, p-chem is an incredibly hard class, and you'll find classes like that in other chemistry, physics, and math majors. I think biology is significantly easier than chem, phys, math, or biochem because all of the classes are memorization and/or conceptual, not so much calculation.
Of course this all just depends on people's strengths, but it's my opinion that a biology major is a series of similarly structured classes (memorization) whereas those other science majors are more diverse in their structure (memorization vs. calculation, at least).
Personally, I chose to become a biochemistry major because a) I only had two years at a university and had to take organic chem during my junior year and b) of the majors available to me in that time frame, biochemistry seemed by far the most interesting. I think I'd have chosen it even if I'd had four full years at my school.
Choosing a specific major because it is statistically more successful is logically backwards. People who choose to to become music majors are people who, for whatever reason, are more likely to be accepted to a med school, should they apply. They possess those desirable traits before they choose a major, and those traits lead them to music. Choosing music just because of it's success in this regard does not magically grant you those traits, and I would argue that being a person who chooses a major exclusively because of your belief that it will help you get into med school is a very undesirable personality trait.