PS2 and DS both sold more units in Europe than in US. These countries matter when you put them together.
I guess for me I could never see xbox as number one globally. It took a colossal fuck up by Sony with price and the time the ps3 dropped for xbox to get ahead and that was whittled away over time. So in this case I still think it is more advantageous for them to make sure they get as much footing as they can in one of the few regions that really supports them.