I would guess that if you're applying to graduate school, you've done a fair amount of reading and writing no matter what your major, so those questions are "tougher".
However, its not the same for math. There is still a general requirement, but the exposure to rigorous math is much more varied. Which reminds me, I kind of remember seeing a "Math for Dancers" class in the catalogue...
Not all people think with only their brain, some people need their body to think. It'd be interesting to see how that actually works from the point of view of someone who math comes to naturally (sans-dancing).
The tests are scaled differently. That's all there is to it.
http://www.ets.org/Media/Tests/GRE/pdf/gre_0809_interpreting...
For what it's worth, this is a trend on other standardized tests as well (including the SAT).