I went through this discovery process myself a bit ago. I think you'll find that the 590's get *much* more positive responses than the 570's, for all the reasons already listed.
Speaking to the fact that a lot of people really seem to have jumped on the 570 bandwagon for games; I think there are a couple solitary and one "comprehensive" headphone review for PC gamer's that shares some of the blame for this phenomenon. As for the latter, a while back, a popular pc gamer hardware site reviewed a bunch of different headphones and essentially labeled the 570's the end-all in gaming headphones.
I'd kind of like to go back and read the review now since I've done quite a bit more research since then, and I seem to recollect that they were all over the map with their choices of contestants. I guess the quality of their competition is pretty obvious considering the fact that the 570's were so highly lauded.
Short version of the opinion I've formed; get the 590's. Also, use the search function to find more threads about this... there are tons... literally.
ps - Try this thread here.