I saw a video doc of Call of Duty 2 and Call of Duty 4 and in both cases they talked about recording real gun sounds. So I would assume that they did that the same with CoD: World at War.
With movies and videogames during sound mixing they usually tweak sounds. Sound reproduction is important when listening to music but movies/games are mixed and effects are added I don't think you can expect to hear realistic sounds.
On a side note - I just got God of War 3 and man does it sound amazing. It's truly an epic game.
