Psion said:
I don't think that's true.
It's true enough. There were plenty of generic AD&D books without a setting label on them, but that didn't mean that Planescape was part of some ivory tower seperate from the rest of the game. The Planescape map of the planes appeared in the revised 2e DMG, even (though I wasn't happy about that).
Planescape was a coherent setting, but it was also "core AD&D." Its monster books defined how those monsters were treated in every setting (when fiends lost the ability to teleport in Planescape, for example, they lost it everywhere, and revised Planescape XP values were applied in other settings), and its take on the planes was the same take Forgotten Realms and generic books (and even Birthright and Ravenloft, for all that they were cut off from planar matters) had.
That said, Dark Sun had its own cosmology in later 2e (though it didn't in early 2e, and Athas also existed in the Planescape cosmology, and the whole thing was somewhat unclear), and the "Historical Reference" series had their own seperate cosmologies most of the time. So it's a little more complicated than Shemeska was implying, but his main point is still completely valid.
Also, Tony DiTerlizzi was and remains a freaking brilliant designer and technician. Even his where I don't like his approach, I have to admire his style.
