Except that it's actually the very same thing for both NPCs and players. The difference being, that NPCs do not care for survival at all. Where a player more often than not keeps the FDS on high priority, so he can escape when things to south, the NPC disables that and a number of other things.
Watch an NPC with power plant at 0%. Some of them don't have any shield recharge any more. They have shut their shield generator down to save power. Most still have the shield generator running, merely the shield boosters are off, which is much harder to spot though.
Except that this is not true. At all. You can test that if you want to. I at some time, when experimenting with a build on an imperial courier, did that testing by accident. My setup was unable to break through the recharge of an Anacondas SCBs. But after a number of SCB uses, the NPC did not use it any more and i was able to kill it. It obviously did run out of SCB charges.
The same can easily be done with chaff. Use a gimbaled weapon, hit an NPC, watch the chaff fly. Stop attack for 20 seconds, then hit it again with. You will find that the NPC runs out of chaff after a while. Similarily, if you have enough patience, you can test their supplies of heat sinks, ammo, etc. And you will see that almost all of them do run out. The one exception: multicannon ammo. That one indeed is coded to be unlimited on NPCs. The reason behind that is that the AI has an issue, where it behaves eratically when it has an empty multicannon in the loadout. The quickfix was to give multicannons unlimited ammo. It was supposed to be fixed properly later, but that proper fix never happened.
That all being said: unless something goes -seriously- wrong, you will never see an NPC run into those limitations. (See my example above: very weird build for the Imperial Courier, which did not pack enough firepower. ) If you need so much time to kill an NPC that these limitations ever come into play, you have bigger issues than these limitations and should address those. And after killing an NPC, you usually simply fight the next one. Which indeed has full ammo supplies again, while your ammo might be depleted after killing just a few dozens of NPCs.
But really, the game has enough actual problems. We don't need to invent some more. Focus your anger on those problems of the game, which really exist.