IGN: "In the midst of the madness of E3 2011, Nintendo Global President Satoru Iwata did several interviews as well as a lengthy Q&A session with Nintendo investors. Among the many topics was yet another question focusing on the number of controllers that could be used with Wii U.
Iwata seems to take both sides, suggesting that while more than one controller could be used, Nintendo is opting to focus on single controller concepts for now. But the reason isn't necessarily a technical one, which is what many have suggested limits Wii U's interface. Though Iwata did dodge outright saying there are no technical problems, the focus of his answer is very telling."