When I took civics in high school (1966) it was universally accepted that birth in a state (or birth overseas to citizen parents) constituted being NBC. When George Romney was a leading contender for the GOP nomination in 1968, his birth in Mexico was never an issue.
In fact, I never heard an argument to the contrary until BHO was sworn in.
That it wasn't made an issue (and I think it was) is not proof that one theory or the other is correct. As a matter of fact, how can you say that the requirement is to be born in the United States and then say that it's okay if you're not?
Is that doublespeak or something?
As for the matter never coming up before Obama, we've never seen this problem in our lifetimes before Obama. Had George Romney won the nomination in 1968, rest assured someone would have made an issue of it. They certainly did in 1916 when Charles Evans Hughes ran for President.