I think this paradigm is a throwback to previous editions, where 9th level fighters were called 'Lords' for example.
My interpretation of the 4e power curve isn't that, in the transition from 20 levels to 30, they've tacked on 10 more levels of awesome, but rather, that 4e level 30 is equivalent to 3.x level 20.
Well, I'm what you might call a 'throwback'. My prefered system is 3.25. I think 3.5 got more wrong than it got right.
The original poster didn't seem to address the question in 4e terms alone, so I answered based on my experience in 1e-3e. If I was speaking of 4e, I'd be speaking of something I really have no experience with or interest in, but if I were going to run 4e then I agree with you about the power curve and would be speaking about something along 12th to 15th level. In any event, whatever the edition, there is some level above which no one with that level is mundane.
So I have no problem with more-or-less mundane NPCs occupying the entire span of heroic tier levels (1st-10th), though obviously a 9th level guardsman will naturally rise to the top.
As I have no real problem with more or less mundane NPC's occupying the entire span of heroic tier levels (1st-4th) from earlier editions, with a scattering of more or less mundane heroic leaders of 5th and 6th level. Beyond that, and I feel like I'm cheating and cheating the players.
And even a 4th level character is something somewhat special, heroes (of a sort) in their own right - the member's of the King's Own Cavalry, elite mercenaries, successful businessmen, leaders of local churches, and so forth. But even so, these will be middle aged individuals with stats generally below those of the PC's.
Paragon tier is where I see the regional movers and shakers - the Knights of the Round Table and so on.
For earlier editions, I'd consider the 'Paragon Tier' to be roughly 7th to 12th level. At that level, you start becoming a force to be reconned with; you begin acquiring fame beyond your local region; and the people in charge start to take notice and begin treating you as something like a peer. Beyond that is truly rare. Above 15th level, and there are countable numbers of individuals of that level across the whole world.
Suggesting E6 as a superior alternative to 4e misses the point that grim'n'gritty = dull.
Well, obviously your milage may vary, but as a player when my character acquires a certain level of power it stops being interesting and starts getting silly. I perfer lower levels of play for much the same reason that the most popular superheroes are somewhat less powerful, somewhat grittier than the 'Superman' tier superheroes like Captain Marvel, Black Bolt, Martian Manhunter, etc., etc. Above a certain level of play it becomes all about the character, and really the numbers start to get meaningless and the play becomes rather cheesy if you aren't careful.
4e models cinematic play better than any edition to date. E6 does it extremely poorly.
I'm not sure we can agree on a definition of 'cinematic'. To me cinematic means, 'consistantly causing the player to imagine things in his head as if there was a movie of the game'. I'm very very very unconvinced that 4e does this well. I'm even less convinced that does emersive cinematic play, by which I mean that the player tends to imagine a first person camera perspective as if he was seeing through the character's eyes. I can't speak for how well E6 does it, but in my experience producing emersive cinematic play is a function of the game master more than the game system so the whole question may be off base. However, I will say that in my experience game systems which are heavily tied to the use of minatures and tactical positioning tend to be poorly emersive at best and non-emersive generally.