Who thinks that when the wii 2 and xbox 720 come out the ps4 won't be released? I mean the hardware in wii was outdated when it was released and the hardware for the 360 is starting to ge old. The ps3 was way ahead of it's time when it was released. It already has blu ray and a cell processor. It's the most powerful of all current gen systems by a long shot. I am thinking that when the new systems are released that the ps4 won't be released after about 2 years after those consoles. The ps3 is already capable of 3d gaming, motion controlls, and bluray. Not to mention the 6 axis in the controllers. The ps3 also has so much more petential to have better graphics as no game has ever used the full power of the ps3. Who else thinks this way?
If Sony doesn't release a new Playstation in the same time frame as the other next gen consoles then it could possibly end up in a worse position than this gen.
At this stage both the 360 and PS3 hardware are beginning to show their age and to say the PS3 is more powerful by a long shot is not supported by most developers who have worked on both systems. I'm not quite sure what the Sixaxis has done/is going to do for Sony's popularity but it's moot as any system can use motion controls. The questions is whether they have a good install base and are well implemented and well supported by the development community in the form of quality software.
Your entire post seems based around the assertion that the PS3 has significantly more graphical potential than the other consoles but regardless it's output is still likely to look outdated compared with any hardware released in the next few years. As has been pointed out already, hardware longevity has historically been related to popularity rather than processing power and I am yet to see anything this generation that makes me think this trend will change.
Having said all that I do think this generation could last a little longer than people are expecting and I don't think any of the hardware manufacturers will have a particular problem with that.