I treat Avbaroy's universe as the Prime Material Plane. The fact that it has more planets in it makes it even more suited, given that there are infinite demons. "Avbaroy" is also used as shorthand for the PMP.
I also like to think there are other planets mirroring Avbaroy's in their own planes, like an entire universe full of planets entirely of lava for the Elemental Plane of Fire. But that's a personal preference.