Oh stop it was just a joke.
Why joke about this?
To drive home the message that while Barack Obama was technically not born a hateable furriner, he might as well be for all that the Republican electorate, and thus Romney, cares. "Nobody doubts my Americanness - I'm a clean whitebread Protestant Ur-American! (Apart from actually being a Mexican Mormon, of course.) Now Mr Obama, on the other hand... he's a Black, you see, and a Black Exotic at that. He's so Unamerican we needed to see his birth certificate."
^You must be another one of those secret Muslims. The Muslim Brotherhood will be running things in no time....
Seriously though it is quite scary how many think Obama is some sort of Manchurian candidate or something.