Some tanks pull with taunt. It's reasonably common if you need a ranged pull and your spec's ranged pull is on CD from the previous pack. I'd agree that it's poor practice, but there's more than enough of that in the average player, tank or no tank. To be perfectly honest if you need your taunt during it's first cooldown after pulling a pack either
1) some DPS wasn't paying attention to your pull and did something dumb or
2) something went wrong with your pull (your attack missed etc)
DPS who assume that the tank's taunt CD exists to correct for their mistakes are some of the ones who create impatient, vote-kick happy, overbearing tanks which those same DPS turn around and complain about. The tank's taunt CD exists to correct for the tank's mistake, if he uses it to save your skin thank him. Break the cycle instead of reinforcing it.