Jer said:
Then what's the point of having them?
I don't mean it to be flip - I mean it seriously. If they're not good for adventuring then what's the point of having them in the game at all?
Because they are there as parts of the setting, as a way to explain in-game where elementals come from, and because it makes sense as part of a medieval look at the universe.
Not every place in the setting has to be suitable as an adventure site, some are good just as background or exposition.
Look at it this way, in a typical modern setting Heaven and Hell are alternate planes of existence, but the adventure will never go there, characters might make reference to them, in a low-magic modern fantasy type game you might even have a demon or angel appear who has been there, but you'd never expect the game to go there. Does this mean that in a modern day RPG, that Heaven and Hell should be excluded because adventures probably won't go there because it's not suitable for mortal PC's?
The Elemental Planes are one of those implied setting elements of D&D that is a sacred cow, and when they remove them the game becomes less D&D, when they remove them and replace them with something with a completely different concept it moves the game further from what people expect as D&D.
Should The Demiplane of Cynosure be removed from Forgotten Realms 4e because it's a place Mortals can never enter and only Gods may walk in? You can't adventure there, so by this logic it shouldn't exist in the setting.