So is this an issue of it being a "bad idea" to give the players nifty abilities that make the monsters do things the DM didn't tell them to? We already have those, they're called spells and feats

Players having an ability to taunt a monster off of teh squishy mage and onto the strong warrior makes perfect sense from the view that the warrior's job is to make sure the mage (and the rest of the party) lives, so why not give him more capabilities that let him do his job better?
If warriors have a taunt-like ability in 4E and you were playing a game set in feudal Japan, the player could use the ability and say that they challenged the samurai's lineage (implying he's a bastard or somesuch), which the samurai would be honorbound to defend, leave the mage alone, and kill the warrior who dared utter such a claim.
He just pulled aggro back off the mage w/o dishing out a big attack, which some people say is wrong. Maybe you're fighting a group of orcs and the warrior yells out in orcish that the big hulking orc who is stalking their healer should come challenge a real combatant and leave the men in dresses alone. A reasonable thing to attack its manliness and insinuate that it can only be successful when fighting weaker enemies. So off it goes to fight a true warrior.
Storywise, both of those examples are very good uses of a taunt-like ability. When you're looking at the book tho, all you see is "Taunt:Use this ability and one target opponent leaves his current opponent and comes at you". Yes you'll have players who just say "Yeah I taunt the guy", but if they're enjoying the game at all and like playing in character, you'll probably have some sort of response more like what I gave as examples.
I don't think a full aggro system where you can just do a Challenging Shout and have every monster in the area come beat on you would work in D&D like it does in WoW, but a singular taunt effect like I described would be perfectly fine. In a combat w/10 opponents it won't make a huge bit of difference, but you can give the healer enough time to get a heal on the one who needs it most while you tie up that opponent.