Everybody knew Osman was better in the middle but we couldn't afford to not play Arteta and Cahill there at the time (and that was arguably Moyes best team). Since the Arteta/Fellaini partnership turned out not to work, Ossie got his chance and he took it with both hands. Bily's unfortunate that he's behind so many people in the pecking order there and we have nobody who's any good on the wing.
Mind you, when Moyes decides to play two defenders as the central midfield pair rather than risk bringing Bily into the middle, I want to punch someone.