I don't agree that Mario Brothers belongs in there, and I think Defender does.
There is no disputing that Nintendo made an empire out of Mario, but that game isn't a major part of it.
With games like Berzerk, Tempest, Galaxian, Galaga, Gorf, Joust, Q*Bert, Robotron and Punchout not even making the list, I don't even thing Mario Bros. deserves a place in the 20.