Machines can be on the market for let's say, ten years
(NES, PS1, GameBoy) ...
but it does not mean that a new release won't be offered during that period.
and with the technology increase coming in at stunning rates, I think these three consoles (X360, Wii, PS3) will have a 5 year lifespan tops in the tech department. And obviously Wii, is already on the bottom rung of the ladder for this generation.
A PS3 will be out of date tech wise in 5 years.
It does not mean people will stop buying it, or it won't be great, but I do not see Sony or any other company for that matter sitting on their hands when the next Xbox, or Nintendo is released.
If the PS3 is Sony's main console without a new machine on the market by 2017 (Which is what they are implying) , I think it would be a huge blunder