sony counts all units, that includes the tens of Millions that were brought back by customers and resold. MS and Nintendo do Not practice this. At the Halo 2 launch, I was one of the first people in line at Eb and the manager and I had a good talk. Hes not anti Sony so dont even go there...
In November of '04 when the game launched, there were something like 85 million ps2s in circulation. The real # was around 70 million, the other 15 million or so were ps2s that broke and resold. Ask any reputable EB/Gamestop manager(assuming they arent semi retarded like their employees), and they will tell you its true, if they arent scared of backlash anyways.
And yes, Xbox is around 25/26 million sold. Not bad considering it doesnt sell anything in japan.
I guess to be fair, even if MS and Nintendo did do that, their #'s wouldnt be higher seeing as the failure rate of their systems is nowhere near as high as the ps2
maybe they figure "why bother, faking the #'s wont help us"