1. Auto-hover does exist, and it's been a feature of helicopters for quite some time. Something about putting computers in an aircraft...So do pivoting machine gun mounts for (some) helicopters. Furthermore, these abilities require each other, to some extent. A pivoting gun is nearly useless if you can't stay still (yeah...try hitting something off to your right while you fly straight ahead...), and yet hovering offers little advantage in a fight unless you're packing some serious heat.

2. (More to the point) It makes sense for smaller & more agile helicopters to have completely-fixed gun(s), since the entire vehicle has more maneuverability, and there's less power/space to mount and utilize a heavy, pivoting gun. For heavier helicopters that lack the same speed and maneuverability, the tradeoff is supposed to be greater firepower (and also perhaps more technology). Strapping on a bigger gun is one thing, but it's no good if you can't effectively aim it.

3. Even if a gunner is required to operate the pivoting gun from a heavier heli, this is something that definitely exists, and with the realism being so well-done in the game thus far, it'd be a shame to leave this out entirely. Of course, it makes little sense to have an auto-hover if one person operates the gun, and the other flies the chopper. Conversely, if the pilot can activate auto-hover and then switch to controlling the gun, just how much freedom does the gunner have in terms of aiming? While I'd love for there to be some freedom (maybe 45 degrees from 'straight forward' in each direction), too much would be both unrealistic and overly-powerful.

Sordidloam also mentions that this setup would be somewhat auto-balancing, and I agree. Sitting stationary is a great way to get yourself killed...unless you have lots of support, or you've surprised your enemy.