Putting out their own hardware allows them to retain control over pricing of their IP, and preserve its value. What people don't get is in the console industry, software sells hardware. Which is why every console MFGer leverages exclusives and Nintendo gets away with putting out underpowered hardware every console generation - the games are what matter and Nintendo having some of the best IP in the industry makes up for it.
As a company, Nintendo has enough money in the bank to offset 10 years in the red. Only way Nintendo would stick their software on a smartphone is if they screwed up 2 console generations in a row and are on the verge of going bankrupt, or they get a CEO who doesn't understand the industry and caters to stockholders who want a short-term profit. As of right now, the 3DS is a success and the Wii U is what Nintendo should be worried about. They've accelerated their first party release cycle, timed to one game a month, to address this. Because games sell hardware.
It doesn't matter that you can airplay to your TV if the only thing you can airplay is some freemium game that repeatedly spams you into spending $10 for virtual gems so you don't have to wait 2 days for something to happen.