One basic flaw in your theory is that Mario sales = Wii sales.
What about those who bought a Wii for Zelda, for Metroid, for Brawl? I think there is a decent chance of having a healthy supply of Resident Evil games on the Wii. And, I even know a guy who wants a Wii for Monster Hunter 3 alone. And I am currently only talking about games that appeal to core gamers not the casuals.
Another flaw is what consititutes a "marioboy," as you are the first person I know to coin this condescending term I am unaware of it's definition. Is it only someone who grew up with a Nes, or does it apply to someone who came along later? If the definition is the later, than there would be new "marioboys" being created after playing SMG.
"But as always, technology refused to be dignity's bitch."--Vance DeGeneres