Well, I don't have a PS3, but I wouldn't mind one way or another. I assume it is technically possible now since Valve and Sony's relationship are slightly less rocky than they have been in years past. But, the money probably wouldn't be there. Can't assume that porting the L4D games at this point would merit the effort to port them and tweak them for the PS3's hardware, when chances are they wouldn't sell terribly well.
Especially when one considers how easy it is *coughpiratecough* the L4D games, and most PCs can easily run the games on even the highest of settings.