I think it's because it still uses the Wii name, the consoles look very similar, and because the Wii had several peripherals/controllers, many people might assume that the new controller is just another addition to the Wii. Just like 3DS, it won't be a huge problem for too long.
That said, Jimmy Fallon's ignorance on the show is inexcusable because first, he is not "gaming illiterate", and second, he has Reggie and the WiiU featured on his show for crying out loud. It'd be like if he had an actor as a guest and said, "You can see him in the new movie... wait, is he in a new movie? I think he's starring in a new movie. You can see him in a lot of past movies...".







