There isn't really a need for more than 1 console if they are all essentially exactly the same, playing the same type of games, with the same type of controller.
Would you buy a Blu-Ray that played all 3rd party movies, and Sony movies, but no Nintendo or Microsoft movies... and then the HD-DVD player to play the Microsoft movies and most 3rd party movies, and then well, Nintendo machine for just Nintendo movies that didn't play any of the 3rd party movies?
That's essentially what people do in the console space.
The reason Nintendo is less successful isn't because they don't have good movies of their own, its because they don't have the bulk of the blockbuster 3rd party movies. Also, more than not, they lack in technology, so while Sony and MS get the Blu-Ray quality movie from 3rd party, Nintendo is still on VHS or maybe DVD quality.
