Quick refresher: the serial comma, also called the Oxford comma, is the comma before the "and" in: "red, white, and blue."
The Chicago Manual of Style, which is followed by most book editors, advocates the serial comma. The Associated Press Stylebook, which many newspapers follow, says not to use it. Per them, it's: "red, white and blue."
Academic types say the serial comma is more correct. (It's true that the AP position is a minority one.) And I think it's just lovely that people have the time and energy to care. Me, I have to WORK with both styles. It's all I can do to remember from one document to the next which style I'm supposed to be following.
It sure would be easier on me if the major style guides would agree on this. But I really couldn't care less whether they went pro-serial comma or anti. As long as I gets paid. (Actually, that's a whole other can of worms. The company for which I do most of my copy editing these days is all over the news for their darling little Chapter 11 stunt -- and they're four weeks behind in paying me! And I'm supposed to care about commas? Woid.)