A quick look at the sweeping wind monk build in Diablo 3 patch 1.08. This build works better while dual wielding weapons because this gives you more attacks per second. More attacks also means more chances for critical hits. Critical hits give Sweeping Wind: Cyclone a chance to produce a lightning tornado, or cyclone, which are the blue whirlwind/tornadoes. These tornadoes do 26% weapon damage.
Sweeping Wind itself also does 60% weapon damage while at a 3 stack. The stacks build based on critical hits. Critical hits are key in Diablo 3 for so many reasons, and this is just one example.