the ps3 natively supports linux back in '04 the IBM team that made the cell processor wrote linux for the cell setup that will be used in the ps3 and it was fast. you think your athlon X2 machines are speed deamons just wait until they bring cell technology to the pc.
I heard a while ago you can install Windows Media Edition on Xbox360. I guess I heard wrong. It would be pretty handy to get a OS running on the Xbox 360 since it is pretty close to the top of the line PC specs.
Everything that has an advanced user interface needs some kind of OS, a OS is just a system that tells something how to operate. I bet even a TV has a very very simple OS for menus and things like that. If the PS3 didn't have an OS then it wouldn't really run games and all the media that you put into it.
running linux on the xbox360 or ps3 will be incredibally fast the cell processors are way ahead of any current multi or single core desktop solution on the market today