So sang Vampire Weekend in 2008.  But it would appear that in the US there are a lot of people that do. 

Grammarians will be delighted by a case in the US where a Portland dairy has lost a US$10m court case that focused on, in this case, the lack of this grammatical oddity.

The case focused on overtime pay and the missing Oxford comma used to argue over the nature of their work. 

So what is an Oxford comma? In a list - say of fish, chips and mushy peas - some people will use a comma after chips.  Equally, however, as many people would not bother. 

So should we care about the Oxford comma?  Yes and no.  I would suggest you use one where it avoids confusion.

Or as BuzzFeed so eloquently put it.

"With the Oxford comma, we invited strippers, JFK, and Stalin."  

Without the Oxford comma, we turn former world leaders into exotic dancers.

"Without the Oxford comma, we invited strippers, JFK and Stalin."