Recently I have been rereading my D&D books from BECMI- 4th ed and various OSR websites.
It would seem that D&D has never really done high level games that well. High level adventures were kind of rare and he ones I have seem to pull out all the stops at least the TSR ones. Things like the Labyrinth of Madness and Return to the Tomb of Horrors seem a little crazy along with perhaps the final encounters in The Night Below.
3rd ed ones are a little different often with less monsters as such but they look crazy powerful on paper, probably not so much with higher level PCs kicking around in 3rd ed. The Age of Wurms and The Savage Tide final installments are a little nuts.
In 4th ed we never got that high but a common complain even from 4th ed fans is the length of time combat took at paragon tiers and how PCs were almost immune to stuff and could lock everything down.
Ironically perhaps BECMI was the most playable version of D&D at higher level as it was very basic and only humans could get above level 10 or so IIRC. A level 20 wizard did not have level 9 spells (had to be level 21) and the Rules Cyclopedia doesn't have that many spells in it for the spellcasters anyway.
Pathfinder is a bit harder to judge but the new Paizo adventure paths seem to finish up in the 15-17th level range instead of 20 like 3.5 ones and on their forums they have admitted the game doesn't actually run that well either at those levels.
Also earlier D&D high level seemed to be above level 10 and in the Temple of Elemental Evil you could fight and have a reasonable chance of defeating a demon lord at level 8/9 perhaps. 2nd ed stretched the levels out to 20 (1st ed it varied by class) and to play epic levels one could get the High Level Campaign book which discussed the problems of higher level play. 3.0 gave us the Epic Level Handbook which was terrible, and 4th ed had epic levels as default but it is hard to say how popular they were.
Anyway using 4th ed terms heroic level to me is level 1-6, paragon tier is level 7-13 and epic levels 14-20. Being blunt I do not really care that much about epic levels or even high level play. I have DMed those levels including epic level in 2nd and 3rd ed but they are usually one of's or short campaigns where the intent is to have fun for a few sessions. I did lose a level 19 wizards to a glyph spell with a power word liquefy spell on it in 2nd ed.
It was kind of funny seeing people get excited briefly about the prospect of level 30+ PCs in 3rd ed and there is a tendency in D&D game worlds to make high level NPCs be stupidly high in level. Raistlin was reasonably sane at level 18 IIRC. In FR of course Elminster at level 29 wizard was outclassed by various other NPCs, Darksun had the Dragon who had powers of a level 30 psion/wizard. Things worked a bit funny in TSR era D&D as a level 18 wizard might struggle to have 60 hit points.
So how important is high level play to you? Do you care about it that much or prefer they get level 1-10 right or at least focus on that? Apparently TSR market research indicated most people did not play at the higher levels although back then it could be due to the way the xp tables worked as progression was very slow. Playing weekly might get you to level 8-10 over a year or more.
Fear is the Mind Killer