Yeah the console business has traditionally never really supported three console platforms at once. Super NES, Genesis and ... Turbo Grafx 16 (odd man out)? Playstation, N64 and ... Sega Saturn (nope). PS2 kinda just ran away with that gen, but the XBox probably hurt the GameCube by splitting what was left of the market and forced Nintendo to go chase casuals, which in the long term IMO has not been good for the industry.
The Wii was the only time it really happened, but that was the definition of catching lightning in a bottle and is something that is almost imposible to repeat on cue.
It's like saying more movie formats (Blu-Ray, HD-DVD, Super Duper DVD, etc. etc.) would be good for the industry ... no it wouldn't be. No consumer wants to have to choose between three or four competing movie formats, and I don't think they want the same for video games either.
Less can be more sometimes.
