I guess Xbox couldn't keep their big advantage for that long, as those numbers are becoming dangerously close.
Dangerously close? Well over 3.4 million behind
And the Xbox was released in Japan & EU about 9 months earlier, a then few less months earlier everywhere else. And let's not forget Sony's 8 million price cuts and 8 thousands alterations to the system. It is never catching up. Sony in general is always getting dragged by everybody.