Didn't the Wii outsell both PS3 and the Xbox 360?
I think Nintendo is doing fine, with a new Pokemon game, New Super Smash Bros in the works, and some other stuff I think they will be doing great.
Another thing is that these guys have been around much longer than the Playstation or Xbox and have had much more effects on gamers than the other ones. Just look at all the Mario, Zelda, and Pokemon fans out there.