The switch to Intel may be coming earlier than we thought? Perhaps tomorrow even?
As to why, well, a lot of movie studios, animation houses, publishing companies, and other various creative industries use Macs for their design work. You can never have enough speed and power for some of those things, and that's what the Powermacs are designed to do. There were alread rumors of duel G5 processors, with duel-cores, being put into the Powermacs soon.
Is Hyper-Threading really a clickable option in Mac OSX?
It could just be a developer screenshot where they bootleged OSX onto a quad Intel PC. The screen resolution is only 800x600. Also, they're running an older build of OSX than what is current (the same as the OSX for Intel developer version, I believe).