I don't know if the stigma is true but the UK and Australia are usually seen has having completely different levels of swearing than here in the US where we are usually limited to fuck, shit, damn, and variants on ass where the severity of that list goes from high to low.
It is usually taken that AU/UK have many more words and/or variations which would mean that common speech would have more possibilities to interject a curse word.
Now that you mention it, American don't get swearing. I don't like hearing them swear either. Americans swearing never sound cheeky, charming, witty, good humoured, playful or anything like that.
I had an American friend at Uni who used to try local swearing or idioms from time to time. "Bloody deadshit!" "Ya reckon?" Relatively tame in the context (bars) he was trialing them. He could never pull it off smoothly, it always got him funny looks. The French, Arab or even Chinese could do it. It sounded fine. Not this guy.
I thought of Australia, but it seemed not worth mentioning, mate. Even with Australia, the UK is just 1.3% of the world's population. That's hardly representative.
P.S. Actually, I wasn't too sure about Aussie speech patterns besides the usual stereotypes. Either way, with its 22e6 population, it doesn't sway the argument.