Let's break it down.
Wii: Gimmicky controls and a low price point made it a strong seller for the first three years of it's existence, but now that everyone has one and they're catching on to the fact that there's nothing besides "_____ Party" to play on it, most of them are collecting dust.
DS: It
still prints money. A couple of years ago Nintendo was insisting that the DS and Game Boy would be their "two pillars" of portables. Then they got smart and let the Game Boy rest in peace. Meanwhile there's a new DS every two years.
PS3: About halfway through it's projected ten-year life cycle, developers are probably reaching the limit of graphical / AI capabilities they can squeeze out of it. So they turned to gimmicky controls to extend the life of the unit, like the Move, which promises motion controls on an HD system. Also pushing 3D TV support as the future of gaming.
PSP: Consistent runner-up to the DS, the PSP Go was a miserable failure, yet there's still an insistence that the system is the future of portable gaming. A constant game of catch-up to whatever Nintendo is doing, seemingly.
360: See PS3, but replace "Move" with "Kinect," and remove the part about 3D.
Also this:

I think that about covers it.