Im Prot Warrior since Vanilla, and I click since Vanilla. AQ, Naxx, BT, Sunwell, Malygos as one of server first kills, Heroic DS as DPS Warr than Tank, hc Sha of Fear, hc ToT and now SoO. Im clicking my main abilities and got bind interrupts, taunt, cd's. Works so well I would not even think about changing to key binds. On the other hand when im on my Mage I cannot imagine playing with clicking, keybinded everything.
So dont judge people who do either way. If theire performance is good why tell someone how should he or she play.