I thought mainly of fighters, and only the ammo for MGs/cannons. I understand that listing all the weapons of a bomber is a lot of work, plus it would be too many lines on the HUD. As of rockets and bombs, you know how many of them you have at the beginning of the mission, so you can easily keep track of your bomb load whenever you drop one. I was thinking mainly about the fighters (although knowing how much ammo your gunnesr have left would be also helpful, but as I said before, a lot more work) and for cannons/MGs only.