Yes the United States is basically the only federation which restricts the franchise to residents of states or equivalent, and doesn't give the franchise to residents of territories. That disenfranchisement is why your discussions about representation and the voting always revert to talking about statehood, as though those are necessarily the same thing.
By contrast, in Australia, Canada, Mexico, Brazil, India, Malaysia, Nigeria, Pakistan, residents of the territories (capital districts and otherwise) have representation and voting rights, as well as those in the principal federal units (states, provinces, etc).
So as a Canberran, I still have full political rights even though I don't live in a state, but someone in my exact situation in the US, like Lexicus, does not have full political rights.