Nintendo considered making the Wii U's tablet-sized controller a separate portable system.
The device simply streams content from the Wii U base unit, but Nintendo president Satoru Iwata told Gamasutra the company debated whether the Wii U controller should work independently.
"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 [base console] system," Iwata remarked.
"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."
Nintendo made that decision for the sake of conserving power. "That means sharper graphics. A battery couldn't do that."
Iwata revealed the Wii U was in development shortly after the Wii launched, with Nintendo settling on the second-screen concept as early as 2007.
Originally the controller and second screen were separate. The LCD screen device would be placed on a nearby table and presumably would not have been touch-sensitive.
Nintendo publicly revealed the Wii U at E3 this year, although the hardware was shown to publishers earlier in the hopes of enticing third-party support - something Nintendo has notably lacked previously. It launches next year.