I dunno, it seems that there are less "smart DPS" than there are "smart tanks" out there. Tanks are forced to think and re-think while pulling, tanking, and using cooldowns--but when shit hits the fan during the fight, it's often the other classes that pick up the slack.
Example: the Hunter who proactively traps an extra add and kites another. The DK who Death Grip-pulls the caster for the Warrior Tank who's got his Heroic Throw on cooldown. The Shadow Priest who MC-tanks an add mid-fight. The Warlock who CCs an add with never-ending Fears.
All these seem to be missing in WotLK with the (relatively) easier dungeons.
The players you are using in your example are maybe tank on their DPS alt's.
My main is a Mage, and it has been since release day. My first priority has always been CC. I think nothing of holding one mob sheeped for 5+ minutes while continuing to DPS the current target.
CC take too much time to apply.
Specially when the mage have to drink because he's getting OOM because the tank is chain-pulling.
The only time I use CC is to dismount rider in UK and Gundrak. Gnome are too small to reach them and I have to jump and time my abilities to build agro on them. Of course, once the mob is dismounted... I break the cc.