You can't sit down and call everything equal. Tim Schafer's work in terms of western games is FAR from common, but hardly has the originality of something like Katamari. And of course Katamari is also a bit uncommon. For the record, I don't agree with the original post or most of the responses.
You can't enter this thread and seriously compare Katamari Damacy to GTA. You're comparing 'unique' to 'mainstream' (as well as game/new series to old series). There are two issues at work here: MARKET and SPECIFIC developers. For the sake of argument, I'm going to look for as little outside influence as possible to guage creativity.
Compare Katamari to an original American game like Psychonauts. By doing that, you can see that both western and eastern devs can output some originality. But I would gently dispute that Schafer's work is less original when you look at American animation. Psychonauts can be easily compared to movies and various 2D and 3D animation like Nightmare Before Christmas and Beetlejuice (both movie and cartoon). Rare for gaming, yes, but not 'out of nowhere' originality. Katamari is far less explainable.
So we see that the comparison between those is a little dubious. Is there, then, a more fair comparison? Beyond Good and Evil, perhaps? I see a lot of animation influence there also. Not a lot of purely creative Western games. Well, let's look at other Japanese games. Nintendo is a specific developer with games that are awash with uniqueness, such as Wario Ware, Animal Crossing, Pikmin, Nintendogs, Doshin, Cubivore, etc. And they're from Japan, but obviously not the norm. Capcom has some unique stuff like Killer 7 and Devil May Cry, also. Then there's Space Channel 5, Seaman, Jet Set Radio, Ico, Eye Toy, etc. Perhaps Sim City and the Sims are decent comparisons to those Japanese games.
That said, western games are creative on a less pure level (like Schafer's work and BG&E). So yes, while all those Japanese games are very original with little detectable influence, and it's difficult to find comparable American software, there are other issues at work. The 'safe' standards in Japan's market are simply different... more open to completely unique games, while that which is safe in America often deals with a license, movie-reminiscent themes, sports, urban themes, etc. But general creativity can be found elsewhere in western games.
Plus, the standouts like Nintendo are opposite to the bulk of developers in Japan (if not the rest of the world) which produce little original content. For example, I almost put Viewtiful Joe and Harvest Moon on here, but there are some obvious influences (comic books, and anime/Japanese RPG's). I mean there's originality in those games, but it's easier to compare originality using utmost uniqueness. And then you have lots of twenty year old franchises (Mega Man, Pac Man, Castlevania...), anime licenses, clones, sports games, dating sims, etc.
My conclusion is that both markets are abound with unoriginality, Japan has more which is purely creative, but the western markets have a lot which is creative on a very general level. Also, the western markets are simply different and allow for less of that pure creativity.