As part of a discussion we had in the media create thread, I am pretty convinced that from a Sony profitability standpoint, it makes more sense to launch in Japan first, even though we all consider US to be the real battleground between Sony and Microsoft next gen.
The PS2 is selling about 80k/month, which is pretty darn low, far lower than US & Europe, even if you were to allow that Japan is ~20% of the worldwide market. Part of that is the handheld revival, but I think the writing was on the wall before the DS was even out. Japan is ready for next generation (or at least, just about done with this console generation)