Zelda is actually a pretty good system seller. It won't get anywhere near the lifetime sales of the big Mario games, but it being quite front-loaded helps sell systems more than 2D Mario ever will. 2D Mario is a game that people (loads of people) buy whenever they 'feel like it'.
Though I wouldn't have guessed Twilight Princess beating the entire software sales for WiiU...
Seriously. I never would've imagined that the Wii U would only have around 75k in software sales globally. Even with the PS3's slow start on the software end, they were only below 100k in the first week when it was just out in Japan. It stayed above 100k in software every week after that through its first March, even though it wasn't out in Europe until the spring.
I can't imagine what possessed Nintendo to expect a 4:1 attach rate with so many ports on the docket, though. Wii owners who wanted those kinds of games have been able to get a PS3/360 for years. Those who only got it for Wii Fit or something wouldn't want stuff like COD or Arkham City on ANY console. They'll be lucky to hit half their 24 million software unit projection now.
Have some time to kill? Read my shitty games blog. http://www.pixlbit.com/blogs/586/gigantor21