Cinematic films run at 24p, 24 frames per second, progressive scan with motion blur to clear up the jutters on moving objects. The great thing about a cinema screen is it's highly reflective surface leaving a distinct after-image in your eye so you don't notice the transition between frames where the screen is blank.
On old 60Hrz CRT's or 60Hrz LCD televisions this transition is much more apparent, especially if showing interlaced footage. Any writing on 540i @ 60Hrz flickers like hell and looks blurry and of low quality. Even if a game runs at 30fps you'll want a nice 100Hrz LCD so you don't notice the transition between the tv's frames, the faster the image refreshes the clearer it looks. That's why I prefer to game at 720p instead of 1080i if using a 60Hrz tv.
COD4 looks great at 60fps, Killzone 2 looks great at 30fps because of their cinematic motion blur. So both games benefit from a tv that refreshes it's image 100 times per second just as much as eachother.
If you think the human eye can only "see" 20 fps, or even a riddiculously low 10fps then please download this video.
http://kimpix.net/2006/12/03/60fps-vs-24fps/
