From my perspective, a person who can shake off a 100' fall or an enormous magical fireball right to the face is, de facto, something out of myth.According to that sense of things, a mythic fighter is more akin to a monster or divine than a normal person or adventurer.
Come to think of it, the most sensible way to rationalize the D&D power curve is to treat all PCs as if they're proto-demigods, every one of them a little Achilles or Herakles in training.
Doing this neatly explains why they can attain class levels while virtually everyone else can't -- at least under AD&D/2e. I realize 3e introduces the possibility of Shoalin Soccer-style high-level NPC classes, and such amusing constructs as the uber-waitress who's tougher than your average grizzled veteran sergeant --a real Eberror NPC, BTW.