The PS3 came out in '06. Was in development long before that. It's easily conceivable. Watch this vid to understand how. This vid uses a graphics card as an example that is actually inferior to the AMD's Radeon graphics technology 5000/6000 series chip that we now know will be in the Wii-U. Still the inferior example graphics card is still more powerful than the PS3.
Wii-U Hardware Specs Explained - YouTube