Who needs Japan when you've already conquered the rest of the world? It will slay Europe and America.
However I wish Japan would be more open to western video games and designers. They're really the only ones who are innovating nowadays. Japanese games have become rather stagnant recently, in the same way that western FPS games have.
But Xbox 360 didn't need the now not so relevant Japanese market to still be as successful or equally to the ps3.. Japan is very proud and arrogant with its video game culture but it doesn't matter anymore since western developers are more relevant now days then most games coming out from Japan. If anything Japan success and games are now local.
I don't think Microsoft is that corcerned about conquering Japan or not... It'll probably be successful in the rest of the world, even though Japan is a very relevant market. So who cares?