Somewhere along the line, I was taught to do it that way, so I thought it was correct. I developed the notions that "and" obviated the need for a comma, and that only the ill-educated would feel the need for one.
I have changed my mind.
I vaguely remember being taught, a very long time ago, that there are two "schools" of thought on this. Apparently, the typical rule in American usage is, "When in doubt, leave it out." The rule in British English usage is, "When in doubt, leave it in."
Commas are widely mis-used in contemporary writing. For example, just the other day I saw a list of places that was written as
"Omaha, Nebraska, Toledo, Ohio, Phoenix, Arizona and Seattle, Washington."
Totally incorrect. Impossible to tell from the punctuation if Nebraska is a state, or a city we haven't previously heard of.
Don't get me started on placement of commas in sentences with subordinate clauses ...