The XBox came out in 2001 and the 360 came out in 2005. Microsoft is the only company (other than Sega) to cut a console's lifespan short like that to try to jumpstart their new console. Nintendo usually has a 5 year lifespan, but has no motivation to kill the Wii with a new console while they are breaking every sales record in the world. Microsoft had a 4 year lifespan last time, and now 5 years later they're releasing Natal INSTEAD of a new console. After all the money they've dumped into Natal, they won't want to release a new console for a while, because that would kill all their Natal money. Same thing with Sony and the Arc.
There is no reason for any of the big 3 to release a new console in 2010 or 2011. Nintendo wants to milk this generation while they're winning, Microsoft wants to milk Natal and their XBox Live profits while they're establishing themselves as a great online community and finally making their first profits in the game business after several years in the red, and Sony wants to milk this generation while they try to break a profit and ride their awesome comeback momentum for as long as they can.
Nintendo has proven that new methods of control are far more important than leaps in hardware technology. New leaps in hardware power target the tiny tiny hardcore base, while new control methods target the whole world, which is now the market you want (compare sales of Crysis to Wii Fit). The last 3 huge leaps in technology lost a ton of money: XBox, 360, and PS3. The last 3 new control schemes made a ton of money: DS, Wii remote, balance board. Notice Microsoft and Sony have learned their lessons and are introducing new control schemes instead of new super-powerful consoles.
Nobody will release ANYTHING in 2010 or 2011. Except maybe a PSP2 and DS2 battle. Maybe.
With that said... by the time the next generation finally starts... all 3 will be at least a little more powerful than the PS3, because costs will have a few more years to decrease. But the generation will be based on controls, interface, features, community, stuff like that, instead of the "RAW POWER" baloney of yesteryear.