Price
80GB PS3 $399
60GB 360 $299 + $100(Battery pack for controller, cable for battery pack, XBox Live) $399 AND you still aren't getting WiFi, BD capabilities, sixaxis, extra 20GB or more exclusives.
On top that look back in history, PS1, PS2 8-9 year lifecycles.
Original Xbox 4 year life cycles, take that into account and the 360 using DVD as it's medium chances are you going to pay all that and then have the plug pulled prematurely.
PSN: EDguila
PS3 library: Motorstorm, Assasin's Creed, Orange Box, Uncharted:DF, Metal Gear Solid 4, Resistance:FOM, Rachet & Clank Future:ToD,
Near future: Folklore, SOCOM Confrontation, BioShock, Little Big Planet, Resistance 2.