That's not really true. The gimmick helped, but the Wii's success wasn't based solely or even mostly on that. Instead, it succeeded largely due to price and appeal to more casual gamers. It's the "family console," and had a lot of games designed to be played by up to four people. Sony and Microsoft had the hardcore market locked up between them, so Nintendo wisely went after an entirely different demographic. It paid off big time for them.
They don't seem to be modifying that strategy substantially this generation, either, they've just added some more social features, new peripherals, and somewhat better graphics hardware. They're still going after the cost-conscious casual market.
The console is $300-$350 depending if you go for the pointless basic package and the games are $60. I don't see how that is cost-conscious.
I'm not really seeing the family focus on the Wii U unless there's more to their online efforts I'm not seeing.