Chaosmancer
Legend
Nah, for the purposes of planescape they should pick lane and then do the lip service thing for the "other cosmologies". They're making a setting, it's better to have some sort of consistency rather than wasting page space on "well that was one cosmology, here's another, we're also going to devote a bunch more page space to a 3rd option..."
People can still make their own cosmologies and tie in planescape, but the actual setting books should have some sort of consistency.
Funny, I was looking at this book called The Dungeon Masters Guide, not The Planescape Setting Book. Why do you think the DMG should be set in Planescape and nowhere else?