Being a non-native speaker I had to look it up. Wikipedia says it's optional in British English but American English encourage, and sometimes mandate the use of it. If you look at https://commons.wikimedia.org/wiki/File:Hello_World_Brian_Ke..., which the author uses in their post - the comma's there. So why the inconsistency?
Yeah, I wasn't really serious seeing as the Oxford comma applies to a list of items. It's something that has never set well with me, the Oxford commma, as it makes the last item ambiguous when not present. So I now just throw out "Oxford comma" anytime there's a question on if a comma is needed or not.