i'm a gamer so i might be biased but why would you require more than the native resolution on the imac?
most games don't run 1900x1200 full graphics very well unless they're old
If your purpose is to play games on your computer, then a retina display would not be useful (at least for now), since even the top video cards are struggling to deliver a good performance on 1080p resolutions.
But then again, if you are on games, you'd probably prefer to use a PC running Windows. Not all games are available for Mac and, even if you run Windows on Bootcamp, you will not be able to have a top-notch video card such as the GTX 580.
A retina display may have other purposes. For me, one of the biggest problems of the Mac platform is sub-pixel rendering of fonts. You may probably have noticed that fonts look blurrier on the screen on a Mac than on Windows. Windows uses ClearType to render fonts: they look distorted, but they are sharp on the screen (and comfortable to read). Mac uses Quartz, which preserves the actual shape of fonts on the screen (they will look like exactly as they do on paper), but they are blurrier on the screen (and therefore more difficult to be read). I consider it a problem because I spend hours in front of the computer writing long pages of text and, therefore, I would like fonts on the Mac to look sharper. And the fonts would definitely look much sharper with a retina display. That's why I want a retina display in first place. Nothing to do with games, though...