How do non-Outsiders respond to other planes?

Question

Would humanoids and the like become outsiders when they travel to another plane, and if not, then why do all of the other planes only contain outsiders, and not material-plane equivalents?

Example: A Hell Hound is obviously a completely different creature than a Babau but they are both simply lumped together as 'outsiders,' so far as I know only because they are not of the material plane. So, when on their home plain, why are they not considered seperate species, such as Dragons and Humans, when they are easily as different from one-another?

Answer 1

No. An outsider is defined as a creature at least partially composed of the essence of some plane other than the material plane. Also see The Planes for pages of detail on the planes and how they work. A humanoid traveling to an outer plane is a "weirdo" or "stranger" but not technically an outsider.

On their home plane, I'm sure Joe Dretch makes more of a distinction between them, but the D&D Multiverse is humanocentric/Earth-centric. So they're mainly "outsider," though you will note that a babau is "outsider (chaotic, demon, evil, extraplanar)" while the hell hound is "outsider (evil, extraplanar, fire, lawful)" - plenty of distinction there.