The Graphical Capabilities of the systme do not really matter in terms of sales, GC and Xbox were significantly better visually then the PS2. PS3 can have great graphics but its the sales that determine how long will this system be around
When the New Xbox comes out Sony will release their system, because it is obvious that 720 will be much more powerful then the PS3, and looking at third parties now they will want as equal console from SOny.
PS3 failed to gain momentum and like N64, GC and Saturn it will make way for another system in few years.
But i can see Wii selling until 2014+ it is a market leader after all.