I've been saying this for years, particularly in the RPG and MMO genres. Japan is largely making the same game over and over again while western devs are trying new things all the time (the openness of KOTOR & Oblivion, the cinematic feel of Mass Effect, the market-busting WoW, etc). Not everything they try necessarily works that well, but at least they're trying new things that don't solely involve using the WiiMote in new and interesting ways.
Really, it comes down to choice and part of it is culture, part of it is the conservative attitude of many Japanese developers. A few notable exceptions being Nintendogs and some of the other radically new DS & Wii games but for conventional gaming, little progression has been made in the past decade by the Japanese.
All you have to do is look at the rise of the sandbox, MMO, shooter, and WRPG genres to see just how deeply western developers have impacted gaming in the past 10 years.