See, to me, that's a "setting consistency and internal logic" thing, not a "fairness" thing.
Yes, but it can become a fairness thing in several ways:
For most of D&D's history, the statement "NPCs don't need to follow the same rules as PCs" was used to justify techniques for disempowering PCs. For most of D&D's history, the NPCs were consistently more special in small or great ways than the PCs and tons and tons of justification was used for this. In my experience as a player, the vast majority of DMs are more often and more powerfully tempted to make their NPCs more special than the PCs than they are tempted to make their NPCs less cool and less special than the PCs. So we regularly see for example, "NPCs can create magic items; PCs can't.", "NPCs can use power of plot magic to build lairs or effect the game world; PCs can't.", "PCs are limited to a certain point buy NPCs aren't.", and in general, "PC's are limited by the rules; NPC's aren't." This can eventually reach the point of, "NPCs don't even need to follow the rules of action resolution like the PCs." For example, "The NPC gets as many actions as he needs to serve the story."
Of course, you don't mean to take it that far, but its a nasty can of worms and it quickly gets out of control particularly if the game gives the GM no markers to represent how much resources/favor an NPC is receiving and doesn't encourage them to think about it or reflect on it. The problem here is that mostly we can justify the NPCs not using the same rules as the PCs because of the high burden this would put on the GM. But if you take it too far, and its very easy to take too far, you end up with a justification for GM laziness.
Another way it becomes a fairness thing is that if it invalidates the player's ability to reason. All game systems need to provide a framework for player prognostication. A player needs to be able to anticipate, at least slightly, the sort of consequences that are likely attached to a proposition, in the same way that in the real world you learn that if you jump you move in a certain way and land in a certain way, that heavy things are usually hard to move, water is wet and so forth. If the game system provides no consistent framework for reasoning, you end up in a situation where the player isn't really capable of taking control of the story because everything that happens seems random, arbitrary, and uncontrollable from the vantage of the player. And in fairness, some GMs actually see this as a positive and run wild, zany, crazy, hugely unpredictable situations as a sort of a power player to keep the game in their control. And also in fairness, that can even be entertaining as long as long as the GM isn't particularly brutal, you were willing to relax and just let the GM run with it, and give back your minimal feedback - which usually amounts to "I hit it with a stick." and "I hit again, but harder."
When the NPCs aren't following the rules the PC's are following, they tend to not be following any rules at all save when it is convenient for the GM. And when you take away "setting consistency" and "internal logic" from the players like that, the players tend to become passive consumers of the setting because they have no choice in the matter.