I'm from England. We pronounce "Worcester" as Wusta. Most of the place names, which end in -cester are problematic for others. Leicester is Lesta and Gloucester is Glosta.As a joke, it also plays on the inability of Americans to understand English accents.
Billy Idol's speaking and singing accent is so south east England, soft 'r', flattened vowels and all!
As someone who grew up with many folks who spoke this way, in Eastern Canada, I have to think about jokes like this, because I distinctly hear Billy singing, "More, more, more", not "Mo, mo, mo" as my American friends do.
Simple example: How do you say the 'r' in Worcester? If you say it as a hard 'r', you're in Massachusetts; if you breathe it out as a soft sibilant, you're in England.