Mark CMG
Creative Mountain Games
I think you've missed his point. If, as ShinHakkaider's example shows, the orc goes all ragey on the party, the players know instantly that the orc has X levels of barbarian. Sure, the very first time this happens, it might be a surprise, but, after that, it's not.
Monsters were built however the heck you wanted in 1e and 2e. If I wanted my orcs to have 4 HD and a 19 strength, I could (and did - Blackrock orcs had a large dash of ogre blood in them). I didn't have to explain it, and, looking at various modules, for example, Tomb of Horrors, you have monsters which are completely divorced from the rules - the Four Armed Gargoyle and the Giant Skeleton.
If I wanted my Sage to know some esoteric bit of trivia, he did. I didn't have to make him a 14th level Expert with the combat capabilities of a CR 13 creature to do so.
I think this is more what's being referenced when they talk about PC's and NPC's not following the same rules.
You make a good point but I also think there is the point that in both cases the GM needs to be surprising the players and not just relying on the same old tricks all of the time. New combinations and variations on old themes, new twists on old tricks, as well as completely new tricks, should often be sprinkled in with the tried and true. Too many of them, though, can just make players feel that the deck is always going to be stacked against them.