From the look of the responses to his tweet it seems it was more outrage in America rather than across the world with people saying the girl in question is a 16 year old American who isn't married....so why try and get a cheap laugh at her expense by making out she's got a polygamous husband...
Americans aren't especially PC by nature but they will make use of their right to free speech, so if you make a crap joke you have to be willing to take the backlash and then not retreat in to saying its PC gone mad etc