Okay, first off, nintendo does not have as wide a variety of game genres as the Playstation. While they try to make Nintendo more of a game system for everyone, Sony has been there, and is known for it. Nintendo has for many years been branded as a system for younger gamers, many in the range of 7-17. However the PS has a much wider fan base, not only from young gamers but from older veterans, this is where the numbers come in. With a wider variety of gamers you have more people buying your units. True the Wiimote, however idiotic sounding it is, is a completely unique design, but that is it's major fault. With a new style controller many people are going to have to learn how to play all over again, and unlike the sensory in the PS controller, which is easily controlled through the shifting of weight between hands, the wiimote is much more awkward to maneuver, and much too small a design for comfort.There is nothing the Wiimote has that the Playstation controller doesn't, and a unique but clumsy design is only going to discourage many veteran gamers. It's another unnecissary modification Nintendo has made to their systems over the years to boost sales.
Next is the graphics, I play a video game and rate it on it's overall appeal, not on gameplay or graphics alone. If a Wii is lacking in graphics, I'm going to be disinclined to explore what it has to offer in gameplay, when compared to a 360 or a PS3.
Over the years, sales of systems are as so:
1-Playstation 2 (with consistent sales rising)
2-Xbox (steady sales during holidays)
3-Gamecube ( sales linger, but not consistent)
This leads us to believe, following history, that Microsoft and sony will continue to head the industry, with Nintendo holding on thanks to a few popular game series. However after E3, there is much much more for Sony gamers to look forward to with God of War II, Final Fantasy XII, Fantasy versus XIII, Dirge of Cerberus, SIlent Hill 5, and many others.
Nintendo won't die off, but don't expect it to outdo the true leaders of the industy: Sony and Microsoft.