This simply isn't true. Games can't get away with fluid motion at 30FPS under most circumstances (contrast dependent. Only extremely low contrast motion will be acceptable at 30FPS).
Movies can do it at 24FPS because film captures motion blur. Every frame is exposed for 1/24th of a second, which means you have thousands of samples over that short span of time composited together into a single frame. This creates a higher effective framerate, smooths the transitions between frames, and creates fluid motion.
Games do not have this luxury. To get the same type of motion blur in a game, you would have to render thousands of frames every 1/24th of a second, then composite all those into a single frame and send it to the monitor. The game would have to run at thousands of frames per second in order to make 24FPS or 30FPS look as smooth as a film.
What games do to avoid this huge problem is take advantage of Persistence of Vision. They run at a high enough framerate, while presenting every single frame, that the human visual system merges the frames together and creates fluid motion. 60FPS is about the minimum for this effect to become solidly fluid under most circumstances. The larger the change in contrast between two frames, the higher the framerate must be to maintain fluid motion using this method (yes, those 120Hz monitors will make motion smoother under certain circumstances if your framrate is high enough to take advantage of them).
Game console hardware is too slow to reliably maintain 60FPS, so those games are locked at 30FPS in order to prevent stuttering due to framerate deceleration. They also tend to enable V-Sync to eliminate image tearing, which means if the game can't maintain 60FPS, it's forced directly to 30FPS. Triple buffering would allow some intermediate framerates, but consoles don't have the video RAM to spare for that, and it would re-introduce the framerate deceleration problem.
Without that 30FPS cap, the framerate would fluctuate up and down depending upon what's being rendered. As the framerate is forced to decelerate from 60FPS to 30FPS, there's a sudden jolt as the time between frames changes from 16ms to 33ms. This jolt is apparent to players, so they cap the framerate low enough that such fluctuations are avoided. Unfortunately, this also means motion isn't as smooth due to the low framrate.
If console hardware were capable of outputting 60 FPS consistently in the titles you mention, believe me, they wouldn't be capping it. It all comes down to hardware limitations.
well it's sort of pointless getting very technical about how liquid 30 fps is. my point is that the frame rate provides a smooth gaming experience. of course 60 fps is a faster, more precise frame rate, so it's always a treat to be running at a locked 60 fps. but in no way should 30 fps be the stuttery choppy mess that mutli-gpu solutions exhibit so often.