I would have included that, but in videogames it's in place for gameplay design purposes. A game becomes much more difficult if you're concentrating on not wasting any ammo, especially in fast-paced FPS games like CoD. Red Orchestra, for instance, doesn't have ammo counts, instead when you reload, it tells you how heavy the mag is (so if you reload and "waste" ammo, you'll eventually come back to that magazine).
As for the shotgun part, I might add that later.
I forgot to say, about fully automatic rifles, I agree with you completely the only thing they're good for is scare tactics, naturally you're going to be more afraid of someone with a fully automatic rifle then a semi-auto or others. But light and heavy machine guns fixed in a defensive position such as on top of a Humvee are more effective.
Along the same lines of rekk's post, ever notice how is some videogames people CONSTANTLY reload? I've played with my friends and after he shoots an enemy he reloads. In other words, he spends about 5-8 rounds on a tiny scrimmage (3 or so people with missed shots and repeated shots) then he reloads his 30 round magazine WASTING 25-22 perfectly good rounds. Some people consider it good to make sure you always have a full clip, but thats wasting ammo, and you won't live very long if you continue to do it.
Right, it generally doesn't make sense in a video game where you reload and that magazine get's added back into your ammo count. Nobody has time to reload their magazines in a combat situation. In Alien swarm for example I like how if you reload and you have ammo left in that magazine it's dropped and subtracted from your ammo count.
Also the whole +1 system in guns applies to nearly every type of gun except for revolvers of any kind, any kind of gun that doesn't have an internal/external magazine. These being single shot shotguns, such as break-actions, and early bolt-action single-shot rifles. And I'm not too sure if whether belt-fed machine guns use them either, I'm having trouble finding schematics on a LMG/HMG to prove that otherwise but my guess is no since you have to discharge before you reload anyways.
