Far Cry 2 does this as well, it even has a Springfield with a left-handed bolt.
The reasons I've seen cited for this trend are:
* Brass flying across the screen is regarded by some as cool.
* Mirroring the guns emphasizes the moving parts as the weapon cycles and is reloaded. Apparently, this is considered to be more aesthetically pleasing.
Neither of those seem like compelling reasons to contradict reality to me, but oh well.