Considering that because the Xbox was so unpopular in Japan that part of Microsoft's strategy was to create special booths in which people could try out the Xbox without the potential embarassment of their family and friends seeing them with one, I'd be mildly surprised to say the least if Japanese developers all started falling over themselves to work with Microsoft.

Chances are, the PS3 will still sell millions more than the 360 based on the popularity of the PSone and PS2, and developers know that they'd be fools to miss out on the gold rush.