Well, do recall that Captain Jack spent a good chunk of his life there and wasn't actually from America to begin with. A little dialect shift seems reasonable.
Oh, I know it's easily explained. Still a funny scene though.
....this would be like having a British guy play a French Star Trek captain. Who'd want to see that?!?!?
Reminds me of something I saw where the writers of American Dad were talking about the character Patrick Stewart voices on the show, the Director of the CIA, who's even drawn to resemble Stewart. Someone brought up the frequently asked question how does a British person become Director of the CIA. To which they answered "this is the same British guy everyone accepted as a French character for seven years, and now you're having trouble with him being Director of the CIA?"