Garthanos
Arcadian Knight
You keep coming back to this idea, so I'll say it again: these kind of logistics have no place in D&D, nor have they ever had. PCs manage to find appropriately leveled foes, regardless of ecologies and logistics. Why, because they're heroes blessed by fate and luck. And because they're the lucky pawns of these things called 'players' who expect to be challenged at a roughly unchanging level. Take your pick.
Oh I do get the wierd luck resulting in heros encountering strange frequency of various occurances... but those really top end big bads do feel more rare if they are a little more rare even for the heros. How many times can buffy stop the appocolypse before she has to fight the drudgery of the fast food business - as many times as the authors can think of an interesting way for it to happen I know

I think you convinced me but I do think there are multiple ways of showing that heros themselves are now big and awesome ... and hewing larger numbers of enemies as long as those fights are interesting could be a solution instead of advancing the level of the monsters that you encounter.
I have always had to design adventures with my players in mind.. if they are more tactically inclined increasing the dangers various ways. If they are less tactically inclined the opposite. I might not have noticed this as I have fewer than the "standard number" of players in my group
I want other ways to even it out...
Lets say the big bads are getting much harder to fight on purpose .. drop the big bads best toy in a lava pit to bring him down three levels (after a quest to find it with multiple lower level encounters) so that he can become more manageable... hunt up the relic with his name in its sights... These methods are much cooler than picking a must have feat. But I guess I dont want this to happen less frequently at heroic level than at epic.
So that doesn't support epic being more difficult.