My fiancée and I have this discussion every so often. I'm obviously a biologist, and she's currently studying actuarial science (which is essentially a tweaked applied mathematics major). We've come to the conclusion that there are two types of knowledge in the world.
Biology, for example, is primarily a discipline of knowing, where the bugaboo is the amount of information we have to learn and retain, and the ultimate goal is typically to make some sort of decision based on what we know (in medicine or dentistry, for example, it's usually some sort of treatment).
Other fields, like math, are primarily disciplines of doing, where the focus is acquiring knowledge not of information, but of procedure. Their goal is to be able to somehow manipulate starting data to obtain the information in which they're interested (calculating significant differences, for example). One isn't necessarily harder than the other, but they're very definitely different.