As much as I love the Wii, I still wanted to see the PS3 become a hit (as well as the Xbox 360 - which obviously is so far).
If it wasn't for the PS2 and Xbox doing so well in the past (and blowing away the Gamecube in most areas), I'm not sure Nintendo would have done as well with the Wii. Competition forces innovation or kicks losers out of the market. The more the competition progresses, the more Nintendo has to progress too.
The last thing I would want to see is Sony and Microsoft to fold because Nintendo would not have as much incentive to keep doing bigger and better things with their stuff.