Actually, people with actual sources within the industry seem to think that Nvidia won PS3\'s GPU contract recently, even if they\'ve been in talks with Sony for years (and probably sending them samples for testing purposes). Remember that it\'s based on Nvidia\'s new architecture which have been in development for some time, and all the work they did for that will end up in PS3\'s GPU.
Anyway, PS2\'s tech demos were shown in Feb 1999 (IIRC), more than one year before the system was finally released. They don\'t need finalized hardware to show something at E3.
I hate how everybody is holding their cards close to their chests though. I want to see something already.