I'm not interested in convincing other that they're wrong - I'm interested in refuting assertions that my game is incoherent, laden with cognitive gaps, etc.But, you're still getting hung up on the why. Why do people take this position? It doesn't really matter. The only point of asking why is to try to convince someone that their position is wrong.
I mean, I think I know what the "why" is - it's because AD&D looked at through the lens of 3E is taken to have established the paradigm of what a RPG is.
I agree more with the second than the first part of this: because it's not that the game defines this - as has been quoted in this thread, 4e D&D has clear rules and definitions.The GAME DEFINES this. Giants cannot knock someone down because the game says so. And if you believe that the game itself defines reality, then, there is no inconsistency. A human fighter can be run through multiple times because the game says that that's okay.
<sip>
Humans can't jump 30 feet because the tradition of the game says that they can't. Fireballs always hit because the tradition of the game says that they do. Weapons MUST have a chance of failure because tradition says they do.
It's because a certain tradition is taken to be what RPGing is as such.