you know the reason for it, well, in real life would you send your soldiers into battle with 5 bullets? because they'll probably die before they shoot 6? and the survivors can pick up whats left?
when they started negative supply, players would do things such as setting up interceptor wings with 2-3 rounds of shots, because they probably wouldn't survive longer. the GM felt that was unrealistic, and set a default level, and set the supply units to automatically pull the supplies up to a default level, creating negative supply
if you think that 20K pb is allot for negative supply, try 500K pb, 1.1M IM, 600K HM, 1M AAM, 700K DM, and 1.2M MI... all at the same time... i nearly went broke, thankfully the 800 pound gorilla with his missiles aimed at me, dealt with even worse
lol, i'm with you, but i also get the GMs point, it makes war more expensive, more specifically, it makes defense more expensive, and creates new tactics, if you think about it.