While the serial comma is not mandatory, it is the current trend. The most recent edition of the Chicago Manual of Style suggests its use.
...if you're in the US. UK grammar rules do not dictate the use of the serial comma
You'll find that many people from other countries where English is the native language don't use it because it's not the current trend there. One British publisher, Oxford University Press, does insist on this comma in its style guide (hence the other title of the 'Oxford comma'), but OUP is alone in this preference.
Wendy
