Commas separating items in a series.

In Rocket Spanish module 2.1, there is the phrase, "Yo, mi esposa, y mis dos hijos."  There is also the phrase, "nadar, tomar el sol, y pesar." I have a grammar reference by Azoulay and Vicente that states specifically that, although English may use a comma before the last item in a series, Spanish does not. And there is no mention of possible exceptions.

Is the final comma used in the examples above a mistake? Or... Are there exceptions that my reference does not mention? Does this rule differ by geography? Is this something that is changing in Latin America because of possible U.S. English influence? Some other explanation?

Thank you.