Feanor said AD&D, and his post is in reference to BG2, so clearly he's talking about 2nd Edition, not 3rd Edtion (which of course is D&D, not AD&D). In 2nd Edition, the planes I mentioned are the ones the deities reside on.
Retroactive change means that technically the change effects 2nd Ed too. It also doesn't preclude the idea that some races came from other primes (because, they did, in fact, do so.) And nowhere is it ever stated that you can't travel between different cosmologies either - portals might be one way to do it, being as they're so common... (Elves, for example, came through a portal.)
But I'm not going to argue with you about it, because it's clear we're never going to agree. I am just pointing out that the Cosmology has changed in 3rd Ed and it's a retroactive change.