True, but well if they just keep a chopper still on some place on the map it'll basically turn into a turret. Or we could add a mechanic where some weapons systems would be offline without the engine running, like the rockets or something or the countermeasure systems (should they add those).
Effectively, this'll just turn a special vehicle (say, an Apache) into a glorified M2 Humvee just sitting in one place shooting its machine gun.
I'm not exactly sure of the truth of this but I found that it's not the amount of vehicles that really makes an effect in games, it how people use them. What I found in games is that there are often people who use the BTR/APC and the T-90/Abrams but stay halfway across the map just sniping people but not effectively contributing productively to the pace of the fight. So basically, if an Apache is just nesting around, it's not really being productive.