I mentioned this in another thread. I think there's reason to believe Retro Studios has two teams: the one working on Tropical Freeze and another still working in secret that was expanded after Mario 3D Kart was released. It was released in December 2011 and a month later Retro Studios was hiring staff from Naughty Dog and Vigil Games. That's convenient. Maybe a bunch of people left and Retro Studios was simply filling those vacancies. Having a team work in secret isn't entirely new to this industry. No one knew Naughty Dog had two teams until The Last of Us was announced.
It's something to consider though I'm not going to get excited over anything. That was why I wasn't disappointed in Tropical Freeze. I didn't care what their game was (though I hoped for something brand new), but really, I just wanted to know what it was, be it DK, Metroid or whatever.
In any case, I don't think it's fair to blame Nintendo and Retro Studios for hyping anything. That's not really how they do things. They get hounded for info by the media and almost always give the standard "We have nothing to announce" line. Any time they say anything mildly different, it gets reported and rereported then ends up being this big deal that people hype up. I really wish they weren't so secretive with their projects, but anyone who buys into the hype does so at their own discretion.