"Opinions vary among writers and editors on the usage or avoidance of the serial comma. In American English, the serial comma is standard usage in non-journalistic writing that follows the Chicago Manual of Style. . . . It is used less often in British English,[5][6] where it is standard usage to leave it out, with some notable exceptions such as Fowler's Modern English Usage."
For instance, while listing computer brands that include Dell, HP, Acer, Toshiba, Alienware, Compaq and ASUS, I wouldn't use the oxford comma. But if I'm listing out speaker brands like Bose, Klipsch, JBL, Bang and Olufsen, and Altec Lansing, I think oxford comma helps to clarify the meaning intended.
Otherwise, no strong opinion, although I usually use it myself.
"There are two hard problems in computing: naming things, cache expiration, and off by one errors."
The comma indicates a pause when spoken, and you need that pause in this particular joke.