As a Brit, I find the use of the serial comma in the U.S. surprising. We were taught in school to write "A, B and C".

Some have argued that using the serial comma removes a source of ambiguity, as in "This book is dedicated to my parents, Ayn Rand and God". Adding a comma here would remove the ambiguity. However it should be noted that using the serial comma can also create a source of ambiguity, for example "We considered Miss Roberts for the roles of Marjorie,
David's mother, and Louise". This sentence would no longer be ambiguous, if the final comma were removed.

The guideline to always use the serial comma is is prefered in the U.S., except in some newspapers (e.g. New York Times)

In the U.K. and Commonwealth countries the normal guideline is to omit the serial comma. The exception here is Oxford University Press, where the serial comma is used.