It is just priorities, and play balance. Every platform in the game has access to its entire ammo load with no chance of breaking or slowing down. Introducing it for one type of platform would only start a problem, not end it. A Cruiser cannot exhaust its 5 inch gun fire at full rate either. None of these weapons were ever designed for the sustained fire they take in the game. Its just a question of where do you start and how important is it to the game.
Quite true. I understand the dilemma, but couldn't one make assumptions and educated guesses based on legit printed sources, testimony from those experienced in said weaponry, and common sense? Those who have fired a belt fed MG, or a larger crew served weapon should be able to comment on reload times. There are loads of film on the internet showing reloads of the Browning M1919 .30 cal MG, Browning .50 cal MG, MG34 and MG42, and I bet if one were to dig deep enough there just might be a film or two of the 3 AA platforms firing away (M16, Wirblewind, Ostwind).
I seem to remember a film of a Wirby with a loader standing inside the turret, being handed ammo on a "clip" from an assistant loader on the ground shuffling back and forth from stacks of ammo crates. If the clips (not magazines, but rather an actual "strip clip" in which the ammo was slid off one end into a fixed magazine) held 10 rounds of ammo, an educated guess would allow for a slight hesitation (1-2 seconds?) every 40 rounds to compensate for that assistant gunner having to shuffle from crates to gunner and a gunner having to fumble with reloading. In any case, I doubt anyone can argue that constant fire of 3000 + rounds is an accurate rendition of the Wirby's ability.
Anyone who has fired an M60, M249, or other belt fed MG can attest to the 50 or 100 round belts used and how quickly the gunner or gunner/loader can reload the weapon. Obviously, the times would be different between a crew served MG with a designated gunner and loader, vs a gunner who had to reach back and grab the belt or box and reload himself. For the vehicle mounted MG's, either a 50 or 100 round box of ammo was used, just determine which standard to go by and implement a "reload" delay of a few seconds.
The M16 AA platform was fed via drums of 200 rounds, then perhaps a hesitation (3-4 seconds due to heft) at 800 rounds fired to swap out drums? There were 2 loaders for the M16.
Start with the gv's, then move onto the aircraft with MG's for defense (or not), but as it is using a wirby is no different than playing Space Invaders at the arcade 30 years ago, just hold the trigger down and fire until you hit.

I believe that this is one area of realism than can be dealt with. If HTC prides itself with its aircraft sim experience and all the effort that goes into that, then implementing a reload time into certain weapons shouldnt be all that difficult, but I'm not a coader so what do I know.