I am not sure you have played WoW if you beleive taunting works in that way, They have added a hate meter to show you how far up on the hate bar you are, the more you use taunt spells the faster your taunt meter goes up, as a paladin I do not even use taunts in the regular way, I have a 150% hate gain when using spells with a holy effect. Not a yes or no binary system, but a percentage system. EQ2 has also added a hate bar so you can see how far up you are, and each hate gain spell tells you a specific number that using that spell raises your hate by, 1500 plus 42 every 3 seconds for example, trust me tank classes are the class I play. If you need I will send you a screen shot of my paladins spell showing you it telling you it increases hate by a specific amount, it is not an either or situation.
Man, taunt
is a binary effect. Taunt is an ability that can miss ( 8% against boss level mobs ), and some mobs are/used to be immune to taunt.
If taunt hits, it forces a mob to attack you for 3 seconds and sets you on top of the threat stack. That's why it's a binary effect: either you hit and the mob attacks you, or it misses ( or the mob is immune ) and the mob doesn't attack you.
Sure, if the second guy on the threat stack generates more TPS than you do, he'll snatch the aggro back, but Taunt is still a binary effect.
In addition, the way threat works in WoW is totally different from how marking works in 4e.
Even the way threat works is fundamentally binary: either you're on top of the threat stack and the monster attacks you, or you aren't and the monster attacks someone else. Only the two highest numbers on the stack are relevant for the purpose of threat.
In WoW, a monster cannot choose to attack another target as long as your threat is the highest on the stack: to take the mob away from you another PC has to increase his threat to 110% or 130% of the tank's threat ( for melee and ranged, respectively ).
In 4e, a marked opponent can attack whomever it likes: he'll just face the consequences for doing so. That's pretty different: WoW creates an artificial resource ( threat multipliers ) that's really abstract, and is really, really hard to explain from an irl POV.
4e, instead, gives the monster a logical reason to attack the "tank": the defender is trained to whoop your ass if you don't focus on him. That's just what happens in real life if you stop caring about the guy who's trying to punch you in the face to do something else.
Threat forces the monster to attack you, marking incentivizes them instead.
Another difference, for example, is that threat doesn't work in a PvP environment, because that would make PvP dull and easy.
Marking doesn't have such a drawback.
(Since it seems that we need to provide our curriculum vitae to discuss WoW, I'll add that yes, I've played WoW for about 5 years, as a tank, with 250 played or so. Not that it should really be a requirement, since, you know, WoW is not exactly rocket science...

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