Nintendo just debuted the Wii U this year at E3, and even then it was mostly a concept presentation. But as far back as 2007, Nintendo was planning for a Wii successor, and even had a second screen in mind. Initially, the second screen would sit on a coffee table, and was planned to be much smaller.
"Considering how expensive screens were then, it did not make sense to have this big-sized LCD," Nintendo president Satoru Iwata told Gamasutra. "We would not have been able to come up with a reasonable price point. We had not decided when we were going to launch the new console, but we knew we needed to be flexible."
For all the confusion following the announcement over whether the screen controller would double as a portable system, that was a decision that the company struggled with as well. "During the roundtable discussions there were such arguments about should we make it capable of being a standalone system or should we make it work only with the system," said Iwata. "We came to the conclusion that this controller is only going to show the images generated and processed by this hardware unit - and sent from the hardware unit wirelessly. That means sharper graphics. A battery couldn't do that."
The leaks that revealed the Wii U before its formal presentation came from letting developers in on the secret, in an effort to attract more third-parties to the system. However, it was a gamble that Iwata hopes will pay off. "For this time around, we are able to expect the top [developers] for the top third parties to make games for the Wii U," he said.
Iwata also reiterated that both Wii and Wii U will be available on the market simultaneously. He suggests that those coming to the Wii now will be late adopters, while the Wii U will cater more to the early adopters at first.