The most defining factor is this, If there was a rematch at Wembley stadium I doubt Mayweather would be able to match Hatton's or for that matter Calzaghe's traveling support.
For boxing? Less of. Other sports it's different. And remember, alot of our country doesn't own passports. So we don't travel out of country for ANYTHING. Not just sports. Our culture has never included extensive travel outside of the country.
Tis a shame. Its quite good out there. The U.S. doesnt have clubs it has franchises, and that ultimatly removes a person from the game.