In the defense of CoD, game balance usually matters more and I wouldn't be surprised if they base it more on the looks and the sounds -- if it sounds more powerful it makes sense in a game to have it more powerful.
In the offense of CoD, yes, they could rate the weapons properly, have it more realistic (if only slightly) and actually make it balanced.
The AA-12 Can shoot from either 70 yards away or 200 yard - I think it's 200. Given that, MW2 is way... WAY off.
Oh, and the AA-12 is an automatic-grenade launcher. Enjoy real life. :D
Just kidding, but yeah, it is, I'm just saying - keep limits but keep it as right as possible with that in mind. :)
- H