Ok, in regards to realism, I was pretty sure Call of Duty dropped all pretensions to realism somewhere between the Snowmobile chase and RUSSIA INVADING THE UNITED STATES...
Fun action game, yes. Realistic depiction of military combat, NO. They both use guns, that's as far as I'm willing to go. Also, I'd probably get killed alot in real combat too, so I'll grant that one, but as I've already discussed elsewhere, reality has some very frustrating gameplay mechanics.
Back to the original point of this post, I think Penny Arcade really said it best with this.
http://www.penny-arcade.com/comic/2009/11/30/
"Double Shotgun Dude is a dog rapist. On this point, there is consensus."
-Though I admit, I'm totally that knife guy sometimes when I don't feel like sniping.