While its true that a 1.2mHz machine can be had for cheap....does that mean that an online game should alienate the other 80% of the population?
I currently use an Athlon 600, and its more than fast enough, but if they doubled the system requirements, Id leave..not because I cant upgrade, but because an online game should not "BE" the benchmark. There needs to be a very broad range of computers that can play it effectively. My 600 is faster than many peoples 800-900 machines because I have tons -o- ram, a expensive video card and optimizations that the average person is less apt to do.
Right now, aiming at anything above 400-600 mHz would preclude too many people. Remember, the 600's were the hot ticket only 18 months ago.