What rule determines usage of "us" or "we" in sentences like "We Americans like hot dogs?"?

I use the informal rule that you always use the pronoun that you would otherwise use if the "clarifying" noun were not in the sentence. So the following sentences are both correct: "We Americans like hot dogs." "Give hot dogs to us Americans." Similarly, "Us Americans like hot dogs." and "Give hot dogs to we Americans" is incorrect. (You wouldn't say "Us like hot dogs." or "Give we hot dogs.") What I would like to know is how to explain that rule using the rules of grammar. I suppose I would also have to ask if anyone thinks that my explanation is incorrect.