It's pretty simple. Without Japan, 360 will not keep WW lead. Wii will surpass prettys soon and maintain that throughout the generation, and PS3 will eventually catch up in by 2009...or so.
I agre totally however Japan Xbox360 has picked up a lot more then I expected it too. If Microsoft could get more Japanese support they could pick it up even more. The xbox360 has sold almost as much(if not more) in the 1 and 1/2 years then the original had in 5 years. That's a large growth, but not enough.
Now they have mistwalker studio which is the guy who invented and worked on ALL the goo FF's 1-6 and left at 7+ which is why the series has been completly losing it for me. Each one worse then the last, there was a time FF would have sold me a system alone, I'm not even looking at 13.
In the end the 360 isn't doing well because the system is mostly shooters etc catoring to the american audience and maybe some Japanese they need more of their style games, clearly they need to look at Nintendo. Rare(known for good or quirky off beat titles Viva Pinata) and Mistwalker are good starts but they need a lot more to get up to good sales.
I have a Japanese friend who swore he'd never buy and xbox during the original(I was the same to this day I have not even touched an original xbox or any part of it and still won't) but the new one had him swearing by it. He went out and bought one and so did a few of my other Japanese friends. Granted this is a small sample but it is a sample and it does show the tide for the 360 changing at least mildly in Japan if they can get out more J-centric games.