Personally, I think that the outcome of this generation will lead all three manufacturers to take a different approach with the next generation.
With Sony and Microsoft, their massive losses in the beginning of this generation coupled with not achieving the marketshare of the Wii will (probably) lead them to focus more on accessable gameplay rather than cutting edge technology. While I wouldn't expect them to be (in relative terms) as under-powered as the Wii was, I would expect their systems to be smaller, more energy efficient and (relatively) less powerful than the PS3 and XBox 360 was.
In contrast, the inability of Nintendo to attract decent third party support was (in a large part) because the Wii wasn't viable for ports from the XBox 360, PS3 and PC. While I wouldn't expect Nintendo to release bleeding edge technology, I would expect Nintendo to release a system that is between 4 an 10 times as powerful as the HD consoles are currently.
Now, which system is more powerful will depend heavily on which system launches last; but I expect the difference between the systems in processing power to be less than what the typical consumer will care about.







