As a fan of both genres, I'm pretty sure I actually played more platformers this gen than FPSes. Super Meat Boy, the Galaxies, VVVVVV, DKCR, Rayman Origins, the NSMB games, Canvas Curse, etc.- we had a veritable renaissance this gen.
More importantly, most games- of any genre- are not worth playing, so I only play a small percentage of the games released each year to completion. As such, the ratio of FPSes to other genres in my playtime isn't anything out of proportion since I'm only playing, what I believe to be, the cream of the crop. I guess what I'm getting at is that the dominant genre on the market shouldn't really matter for any one consumer buying selectively. If the bulk of the market shifted to a different genre, you'd likely see plenty derivative, poorly designed games in it and would end up sticking with just a few staples while forum goers then began to complain about it.