Personally, I think it is a matter of available processing power ...
In both cases you're going to try to emulate the Emotion Engine on your CPU while mapping the Graphics Synthesizer to your GPU (in the case of the PC you're abstracting this through Direct3D or OpenGL calls). When you have completed this, if you want to boost resolution (add AA or AF) this is directly related to processing power on your GPU. Unfortunately for Sony the PC has had a crushing advantage in potential GPU power since nVidia returned to multiple graphics card set-ups with the Geforce 6; there were a few Quad SLi Geforce 6800GTX setups which should be far more capable then the capable then the RSX in the PS3.
This all means that these guys can generate screenshots of PS2 games running at 1920x1280 with 16xAA and 16xAF because someone has a dual Geforce 8800GTX setup and is willing to show off.
