I'd just like to add to Your Mother's fine comments on the subject. The idea of dropping the comma before "and" in lists of more than 2 items was popularized by newspapers motivated by cutting costs to increase profits. Although the professional writers and editors of newspapers have been sources of some fine guidance in the art of writing, they quite simply got this one wrong.

Some respected producers of style guides have previously adopted this no-comma rule because it came from a respected source (professional writers). Other respected producers of style guides have tried to stradle the fence and say that such a comma is optional but should be used when it makes the meaning clearer. But this latter stance only allows for the removal of ambiguity in one direction, not allowing the absense of the comma to convey any meaning.

So you really should only drop this comma if you feel that you are saving more in ink/paper/bits than you are losing in power and clarity of expression. For me, the exchange rates among these currencies makes that decision effortless.

I'd be interested in well-reasoned arguments for the eliding of this comma. The only ones I've heard to date fit in with our most recent poll topic, such as "Appeal to Authority" or "Appeal to Popularity".