ExploderWizard
Hero
The answer to "What doesn't he understand?"
In my view, bringing up questions like "What if two minions are fighting?" as more than a goofy question shows a lack of understanding. There have been a number of posts by other people in here with similar ideas to this. In my book, they don't get it.
For those of you who say, "The world exists outside of the PCs and everything is exactly as powerful as it would be against the PCs.":
How do you play the game? At all? You would have to run your own mock combats for EVERYTHING that happens in the world. Do you roll Stealth checks for thieves to get away from the guards before the PCs ever show up? Or do you handwave it? The little quote about this is "If an NPC climbs a tree, and a PC isn't around, does he make a Climb check?" Of course not. It gets handwaved. "Why did this happen? How did this work?" It did because it needed to.
Minions are the same. HP are much more abstract than some people seem to understand. You can say, "I don't like having my PCs able to 1-hit something." That's fine. You don't like a part of the game. But don't add, "Because it doesn't make sense."
Why don't minions make sense? You answered this yourself in this post actually. NPC's engaging in activities without the PC's is different than the minion issue. Minions interact with the PC's directly and are painfully obvious gamist constructs due to this fact. HP as an abstract concept I understand. A monster with 40 hp doesn't take 40 points of physical damage to drop perhaps. HP represent combative power and is a universal measure of combat effectiveness.
A minion begins an encounter with almost zero combat effectiveness combined with strange BS immunities. The problem is amplified when minions are mixed in with regular troops. Lets say a wizard fireballs a mob of slobbering goblins. Some of the goblins are new minion reinforcements and some are wounded troopers from earlier in the battle. The blast of lands among the goblins. Goblins with 3 or 4 hp die on missed attacks but the 1hp minion ignores the damage. Why?
1) The minions thought that dying before getting to attack would be unfun.
2) The minions used the other goblins as shields.
3) The minion rules were not really thought out.
I gotta go with # 3 FTW.