|Audrey Hepburn could pose like a comma.|
As someone who was born and bred in Canada, works as a copyeditor (and literature/journalism professor) in the United States, and writes for a (gorgeous) British magazine, my understanding is this:
In Canada and Great Britain, the Oxford comma is NOT used. In the United States, it IS used, EXCEPT in journalism.
It's confusing. Fortunately Boy George wrote the song "Comma Chameleon" to help us out (wink):