I think we're looking at the fragmentation of the gaming market - with the Wii and DS going for casual gaming, while the PS3 and 360 going for the traditional (hardcore gamer).
What are we in now, the 7th console generation? If so, Wii offers generation 6.5 hardware and probably generation 8 controls/interactivity, while the PS3 and 360 offer generation 7 hardware with generation 6 controls/interactivity.
I think with the Wii Nintendo decided that rather than try go grab the hardcore gamer first and then aim for the casual market as the price of the machine lowers (the traditional tactic used by Sony and Microsoft this generation and which Nintendo arguably failed to do with the Gamecube), they decided to straight for the casual gamer right away with the low price and unique controller and then as the sales mount up and third party support builds, get the hardcore gamers too as 3rd parties develop hardcore gamer games due to the large installed base.
Systems Owned - High end PC, Nintendo DS, X-Box 360 and PS3
PSN and 360 ID's - Tommo1975
