Cheat means to violate the rules deliberately (http://dictionary.reference.com/search?q=cheat). In the case of FutureMark's products (or any benchmark for that matter), the companies are expected not to "optimize" specifically for their benchmark.
Then both NVIDIA and ATI are cheating. Like it or not, both of these companies "optimize" for this benchmark. This makes a perfectly level comparison using a synthetic benchmark very difficult, no doubt about that.