If Earth is connected to the Great Wheel, then where do the Petitioners of people of Abraimic religions (Christians, Muslims, and Jews) go following death, given that God hasn't been (and my understanding is, won't be) given a home plane?
My postulation: nowhere in the known planes. And that annoys the planars (especially Guvners) to no end.
I think the game designers wanted to limit real-world mythological representation mostly to beings which are contemporarily considered mythological. E.g. most people today don't believe in Dionysus, so it's pretty safe to do what you please with the drunken guy without worrying about offending his faithful (sorry if any of you are priests of Dionysus). Plus, ancient religions held many gods, and the possibility of more, while Judaic religions hold there to be one God, and anything else is blasphemy. God (the Judaic God with a capital "g") exists alone, and in these religions there is no interaction with other entities.
Of course, most of this gets thrown to crap when you consider the Hindu religion, which is a still-active, polytheistic religion that actually has some deities appearing in D&D. I guess the game designers figured there wouldn't be too many Hindu D&Ders, or at least not enough to complain.
If it interests you, there is an adventure available for download (maybe at the Mimir) that details what happens when a deity "thinks" that he is the only power. The misguided deity has some strong parallels to the Christian God, so it should probably be for non-Christian or open-minded players, but it's pretty interesting. Basically, this power from Mt. Celestia sets forth the idea that he is the only power in the multiverse and that there are only two Outer Planes: his realm and the Abyss. He focuses all his attention on one Prime world, and anyone from here who doesn't follow his religion, regardless of actual alignment, ends up in the Abyss after death. The influx of non-Chaotic Evil bashers in the Abyss ends up weakening the borders of that plane and diluting it, so that tanar'ri end up "slipping" into other planes, including Sigil. The players have to put a stop to it all.
Additionally, someone set up a Judeo-Christian RPG set in the Holy Land. I don't remember, but it may be called "Crusaders."
I always assumed that the Petitioners that didn't worship any of the known powers (or were faithless) simply ended up in the plane that most closely represented their alignment. It was their actions and mindset, not just some silly faith, that determined where they would go.
I always opted for this idea because it steps on A LOT less toes than something stupid and narrow-minded like, The Faithless end up fused to the walls of some fiendish fortress for all eternity. *coughforgottenrealmscough*
God lives in Mount Celestia. No higher than Solania, in fact. I see absolutely no reason why he should be different from any other deity.
I seem to recall from previous conversations that Yhwh/God/Allah doesn't grant spells. This means that either he is not an extant deity as of yet (his formation in the Outer Planes probably impeded until now by the barrier) or else is an over-power. In either case, his followers will be sorted by alignment rather than into a deific domain.
Personally I like having a heckuva lot of formerly employed aasimon roaming the planes trying to revive Him, as he died without his followers to worship Him. Guess I just like tattered white robes and genuinely bloody halos.
If Christianity was applied to Planescape, wouldn't the Judeo-Christian God of the Abrahamic religions exist in Chronias - the uppermost layer of Mount Celestia? I mean, that is where Ahura Mazdah of the Zoroastrian religion/mythology exists. After all, in the most anthropological (and mythological) sense, Ahura Mazdah is the closest thing Planescape has to offer in regards to something like the Judeo-Christian God.
Well first I am not to sure whether we should really concern ourselves with real world religions, I can think of people who would see that as a offence of some sort.
But then it IS a good idea to state that none on the planes have an idea whether our religions are in fact the real ones.