All this comes from Creamsteak's concept of Living EnWorld as a character-driven enviroment, once characters reach high level. I think we may have bandied about a loosely-defined NPC limit about a year and a half or so ago, but we pretty much agreed that there would occasionally be exceptions. For example, if there's a 9th-level cleric in every sizable town who can case Raise Dead (to say nothing of a 13th-level cleric who can Rez), there isn't much point in traveling north, is there? Some themes we discussed were that higher-level NPCs might be out there, but they weren't very active so far as generating world-shaking events. Patlin's Fey Lord is a good example.