Seeing as how Skyrim is laggy as hell on an nvidia 7900 GTX, (That's what the
PS3 uses, still) I don't think this is true anymore. (Specifications for the 7900 GTX:
GeForce 7 Series - Wikipedia, the free encyclopedia) (Older PS3s use the 7800 instead.) But, then again, nvidia is known to have trouble with texture rendering, unless you get the latest GPUs (560+) which have Dynamic Tessellation / Texture support. If you want to go with an older AMD, be my guest. Just remember, I gave you information, when your MMORPG starts lagging like crazy. Not that it matters even with a GTX 470.
This is why I'm giving up on Desktops when I need to search for a new machine. Honestly, the graphics cards are getting better and faster than what video games can catch up with, finally.