And I am willing to bet you that he can sell at least one
Okay, even if he can sell one, so what? That "one" is pretty arbitrary.I can bet you if Arrington put up a preorder page of a product called SUPER-CRAP, he could sell more than one. Again, so what?
The end goal is not to sell one. It's to build a successful business. And that requires significant(even if unequal) contribution from both prod dev and marketing.