Fable 2 is a game than many xbox owners played (the fisrt part), it sold 3 millions, so, mass effect was a new game, with more installbase + well know name, would be more like 700 - 900k.
End of 2011 (made 02/01/11)
Wii: 99.453 m
Xbox 360: 67.837 m
Ps 3: 60.726 m
Best Games/Serie of the Generation