Reasonable on 08 March 2010
Here's what good old IMDB has to say - note most films have tons of stuff like this and artistically it's considered fine.
The director wanted a key character to be playing a violent combat game at a certain point and chose Gears/360 to have the (I'd say dubious in context) honour.
From IMDB:
Anachronisms: There is a scene where Specialist Eldridge is playing Gears of War on an Xbox 360 when Colonel Cambridge enters the room to counsel him. The Xbox 360 was first released 2005; the game Gears of War was first released in November 2006. At the beginning of the film a title card specifies that the setting is Baghdad in 2004.
Try to be reasonable... its easier than you think...
