The issue of firing up to your maximum weaponry was settled soon long long long ago. If I remember correctly, and it has been a loooong time, it was settled in the original forums, before the SG forums, before the black backed BFG forums. In essence, you don't have to fire all your weapons. If you have 12 WBs you could decide to fire only 6 if you wanted to. If you want to split your fire amongst multiple ships then you need to take a test to do so.
Similarly the HA ruled that you could fire less than your maximum torpedoes. This was to allow people to sneak them through holes in their line so they didn't shoot their own ships, though there are other reasons why someone might want to do so. At the same time the HA said that any unfired torpedoes were lost.
It comes down to how the game treats ordnance. A single salvo of torpedoes is treated as a single marker, regardless of strength. Whereas a wave of AC is made up of individual markers. Therefore once your torpedoes have fired, at whatever strength, they must be reloaded before firing again.