I think Sony will have the new playstation out by 2011/12, the new xbox maybe a year before, but i reckon the Wii 2 will be out a lot sooner than both of them. Sony mentioned the PS3 having a 10 yrs life span doesnt mean 10 years before the PS4, be like the PS2 is now, and thats still going to be around for another couple of years. For some reason I think the PS4 will have a cell cluster to do all the GFX/CPU work, good thing about the cell is thats its designed to be used as a multi CPU environment and is now being implemented in many super computers in such a way. This may also make it slightly easier for developers to work on the PS4 as they will be used to the cell by then although not as a cluster. IBM already have the cell running at 6GHZ so 8 cells running at 6Ghz would be a pretty powerful machine.
Still think we'll see a new DS and new PSP before any of the next gen consoles though, depending on how well sales are going.