Its not a perfect relationship but you tend to see a (rough) doubling of processing power at the same energy consumption and manufacturing cost whenever you shrink the size of a transistor in half. Moores law states that you will double the number of transistors on a silicone chip every 18 months ... If you take both estimates together you have a rough doubling of processing power approximately every 18 months, and over a 6 to 7 year period you would see an increase in processing power somewhere between 16 and 32 times.
Now, in raw terms the XBox 360 and PS3 are roughly 8 times as powerful as the Wii and 2012 is a 6 to 7 years difference between the release of the HD consoles and the release of Nintendo's next generation system. Now, using our rough estimates this would put a similar console to the HD consoles that is released in 2012 at 128 to 256 times as powerful as the Wii, and a system similar to the Wii as being 16 to 32 times as powerful as the Wii.
Whether or not Nintendo makes it to the 100 times as powerful level isn't really my point, when you move from the Wii to a console which could be 2 to 16 times the processing power of the HD consoles you really face a paradigm shift in how you develop the underlying software for your games.
