Omitting a serial comma (sometimes called the Oxford Comma), however, is a mistake committed by all too many professional writers. Simply put, the serial comma separates items in a list. For example: Blue, green, and red are colors of the pixels in a computer display screen. The colors are a set and a list; a concatenation, to use a big word. I mention the computer display because today's rant stems from yet another paid writer for a tech blog who doesn't seem to know about the serial comma.
When the first iPad made its appearance in our house, it quickly became apparent how intuitive it was for the kids to use (for the record, mine are aged 9, 9 and 12 so they are reasonably responsible with fragile gear so long as it's in a protective case) [Moon, Brad. "The Case for Buying iPads for Your Kids." Gizmodo MAR 19, 2012 7:14 AM].Are his kids aged 9 and 12, written about with a folksy, conversational pause, or are they ages 9, 9, and 12? (I won't get into aged vs. ages.) How many children does Mr Moon have?* Without the proper use of a serial comma we won't know the answer, though we can probably guess it is the latter situation. Most people don't remember back to Elementary school and the serial comma lesson, yet without its proper use the writer's intent can be seriously led astray.
Comical, yes, but I believe it gets the point across. A comma is a pause. Read aloud what you have written to tell if it "sounds right," especially if your message is important. Your tone can remain conversational if that is appropriate for your audience, but don't become so lazy with the punctuation that you lose clarity.
"Going, Going, and Gone?: No, The Oxford Comma is Safe ... For Now" by Linda Holmes
"Michael Hogan: Vampire Weekend's 'Oxford Comma,' Explained" by Michael Hogan
"A Snarl of Serial Commas" message board discussion on the A Way With Words Website.
* Lately I've adopted the British style of titles, omitting a period after.