You are all forgetting that the entire dungeon system is built on the basis of rewarding higher level players who queue up for earlier instances to aid new players.

There can never be a reward for some elite version of those dungeons that would draw people away from the current dungeon instances, which are an integral part of game play.

None of the other MMOs mentioned here require you to engage in a dungeon instance as you level, so they can get away with such features.