At the very least to even the playing field. Everybody has a computer or two in their house and chances are they are not an order of magnitude apart in performance, as is true of video cards. Also, there will be less "cheating" by pros, because the playing field will consist of only one type of player - the CPU.
It's not an even playing field.
- What about those who have 2 computers in a house instead of 1?
- What about those who have access to a network of computer (100's) instead of your home?
- What about those with thousands of computers on a botnet?
- How is it currently not an even playing field when you can currently go and buy a graphics card?
- Why is requiring you to buy a graphics card more unfair that requiring you to buy a CPU?
- How are pro's "cheating"?
- How are pro's prevented from cheating if limiting it to only CPU?
Your notion of fairness is retarded.