Vyvyan Basterd
Adventurer
if it was available for the BBEG NPC or the Monster, then the feat/spell/thingy was available to the players, or should be able to be replicated by the PCs.
[Emphasis mine.] The if I am referring to is classes/feats/spells.
That seems more like a play-style issue than a game-design issue. I've never run or played any RPG with such an assumption in place. So, while I can certainly see why some players might have developed such a sense of entitlement, it isn't a part of Pathfinder as far I can see.
Could you give an example in 3.5 or Pathfinder RAW where a given class, feat or spell is available to the NPC or Monster and not available to a PC. I'm not talking about feats that require a physical attribute like wings or Large size, just a feat/class/spell that explicitly says DM Only.
since 3E didn't explicitly say that DMs have to play by the rules,
AD&D opponents (mainly monsters) and 4E opponents are explicitly built using different rules than 3E equivalents. This set up an expectation in many players' eyes that the DM would now have to follow the same rules they did. Sure, you can always point to Rule Zero, but disappointing your players by using it as a crutch for every time you want to buck the paradigm isn't exactly a good idea, IMO. Everyone at the table needs to be satisfied with the game, not just the DM.
Warning, some may find the following maudlin ramblings not to their personal taste. So I will hide them away in a spoiler block so as not to offend:
[sblock]I wasn't satisfied with the 3E paradigm and that led to my abandonment of it. Luckily, my players are just as satisfied overall with the shift to 4E that we are able to reach concensus of play. It could have also gone the direction of one of them stepping up to run 3E or PF and me being satisfied participating as a player.[/sblock]