It strikes me that people who try to hype up the PS3's emulation under linux have never tried it.
I have, ignoring the large amount of tweaking to get a distro working properly with the PS3 hardware/HDTV (I've tried yellow dog and ubuntu), the emulation just isn't very good.
At least with an NES emulator you'll be able to run a game at full speed. However, good luck getting it fit to the screen properly or get it working with PS3 gamepad (again more tweaking). Other systems, SNES, GENESIS, don't have an emulator that is going to run at full speed on the PS3.
Other software suffers from the same problems, lack of selection and slow performance. Maybe this will change in the future, but right now linux on the cell isn't that great for desktop style apps. Yet I see it hyped up all the time, but people who either haven't bothered to try it, or are fine with a lot of tweaking for a extremely sluggish emulation/desktop experience. Just because you can do it, doesn't always mean that it is worth doing.