In the PR news release about its official expansion into Latin America, Sony states:
...already consisting of an active worldwide install base of 21.3 million PLAYSTATION(R)3 (PS3(TM)) computer entertainment system ...
That number is about 1M more than what VGChartz has the PS3 listed as selling. So there are three possibilities.
1. VGChartz has undertracked the PS3 (a less than 5% error).
2. Sony is quoting sales to stoores (which is what they know).
3. Sony misspoke (which happened by 10M on the PS2 sales).
My money would be on No. 2 -- but any of these or a combination thereof is possible.
Mike from Morgantown