Speaking of Wimbledon, ignorance of the "comma of direct address" apparently isn't confined to the States.
Just as countless American teens write "hi mandy" and "hi jason," as though Mandy and Jason were "hi," one of the British tabloids lent support to adopted Brit Greg Rusedski by printing a full-page sign for spectators reading "COME ON GREG." Comma. Please. Otherwise it's the title of a gay porn movie.