Is 120hz for games so essential ?
I'm not into games, but 50hz interlaced or 24prog looks fine for films, indeed with tv's frame interpolation you can get a smoothed annoying soap opera effect at faster rates,
so. moreover, you need a black frame insertion to help the brain break up the succession of images, even with fast pixel response times.
Better games hardware should be improving the rendering/texturing quality at any frame rates too, do games already offer a trade off ie. do you want image quality OR frame rate
Movies, whch should be the pinnacle of rendering (better than games) often look poor even though they are 24fps, which suggests processing power there should be targetted at quality not frame rate.