Are the Retina MacBook Pro 15" suitable for PC (Windows) gaming?
There are a great many games that support 2880x1800 and most of them support 2560x1600 (Cinema, Dell, and HP 30" resolutions)

Windows 7 &amp; 8 don't support the quad-pixel and dual-pixel modes of OSX, they do things a bit differently. You always have the 2880x1800 resolution, and simply select larger font size (150% in my case). 

Most games will work out fine, but some will need some tweaking (mostly selecting the option Disable display scaling on high DPI output on the compatibility tab. 

If you regularily use an external monitor i would reconsider the retina display. Having upgraded to it from a 17" i5 I found out the hard way that neither OSX nor Windows can display different DPI to 2 monitors, hence my 30" Dell is pretty much useless.