No you are right, Oblivion got better textures, AF and a resolution increase (+better framerate) when it was ported to PS3.
But then again Oblivion GOTY 360 ran at an even higher resolution (720p) with 2x AA, about the same framerate as the PS3, and had better textures(albeit 8x AF on the PS3 makes it seem other wise), shadows and others things (water).
I doubt Oblivion is a showcase of any of the consoles strenghts or weaknesses, Bethesda Softworks has never been known for their technical skills, their PC games all run horribly (it took like 1-2 years before you could max out morrowind and keep a decent framerate, and that wasn't exactly good looking by then).
The PS3 version gains are not because the PS3 is better in any way, but because Bethesda has a very finished game that they just have to tweak for a year, just like the Goty edition on the X360 got improvements because of more dev time spendt.