It seems like the rules are MORE important for the smaller (LW, MW) classes, where a small advantage could make a big difference in lap time. The big bikes have so much HP, the rules matter a little less...for most of us mere mortals anyway.
The rules are important though, as someone else pointed out, it's the only thing keeping blatant cheating from going on.
SS is an important class, it allows riders on a budget to be competitive in at least one class. Big HP is expensive, especially down here in FL where big HP also usually comes with gas charged forks, carbon wheels, etc....