First off, the Wii U does not sell. 13 million copies is absolute rubbish. It makes no sense for them to support the Wii U with a ton of new games with the NX just around the corner. Luigi's Mansion 3, which is rumoured to be an NX launch title, is rumoured to have started development as a Wii U game. How many others might there be? I've never understood short-term thinking. All the signs seem to indicate that the NX will get proper third-party support, and as a 2017 console it might actually be able to compete with Sony and Microsoft's next-gen consoles in terms of power. That means 5-6 years of awesomeness. So what if we're getting a two-year draught because of it? We're almost at the end of the draught, anyway.
Now, Zelda U. First off, Twilight Princess did not gain much from the delay because it was being ported to the Wii, which has a completely different type of controller. The Wii U and NX versions of the next Zelda, however, are likely to be identical. Which means they'll be working on the gameplay, and the longer it's delayed the longer they'll work on it. As far as E3 is concerned, unless they do something similar to the FFXV reveal event, they're not going to talk about Zelda U for an hour! Besides, they said it'll be the only PLAYABLE game. To me that seems to indicate that most of the games shown will be games that won't be out for a while. That rules out Wii U games. There might be some focus on 3DS games, but I bet that after Zelda the main focus will be NX games. They said the console won't appear at E3. They didn't say there wouldn't be any NX games. In fact, Zelda U is an NX game. Besides, just showing the games would be a good way to reassure gamers who are worried that it'll rely on some gimmick.