mmo's have terrible graphics... don't try to pull that one
they have to have bad graphics, when you see a few hundred people on 1 screen, there will be lag if you use high end graphics
also they avoid doing it because they want more than the top 0.0001% of pc's to be able to run it
WOW does so well because it is a popular game and almost anyone could run it compared to most other pc games
how many times do you see blizzard or who ever makes WOW complaining like a cry baby about people pirating their game?