We actually never implemented threat decay. We're not sure we'll need it.

The bottom line is that being a good tank is a mark of pride for tanks. It's not fun to do a job well that any guy off the street could do with no practice or experience. Getting better at your job is a major motivator for players to play.

Threat is part of that. Back in the day, you got excited when you had a tank who knew how to generate threat. It was a source of bragging rights for the tank.

So just autoattacking, or just Thunder Clapping, shouldn't be enough for you to never worry about threat. You should have to pay as much attention to your rotations as an Affliction lock or Frost DK needs to do in order to be competitive on meters.

We don't want to go too far though. While it's not asking much for a mage to wait a few seconds before unloading with everything they have, it's also not fun if you feel that tank threat is constantly throttling you. In particular, we're trying to clamp down on the situation where say at minute six or seven despite everything the tank can do, the dps start to creep up on you. Vengeance was implemented almost entirely for this reason -- it helps keep tanks scaling their threat as dps classes gear up.

Finally, we don't want the tank to be solely at the mercy of others to generate threat. We don't want abilities like Tricks of the Trade or Misdirection or dps classes using their threat drop abilities on cooldown to solve the whole problem for the tank. All of those abilities still exist, but they won't turn a bad tank into a good one and they won't make a great tank feel 100% at the mercy of others.

Q u o t e:
It shouldnt be. The mark of a good tank should be going into a situation where other tanks die and you survive.

Ask just about any dps what the mark of a good tank is and they will say one who holds aggro.

But thats not it. Good tanks survive. Bad tanks sacrifice stats for unneeded threat just to impress a bunch of dps who care about nothing but how big their numbers get.

Thats one of the things i liked about wrath, threat can easily be worked around and it gave good tanks the ability to show what is most important to tanking...survival.

While it's probably true that a really good tank can cover for bad healers, good healers can also cover for a really bad tank. It's harder for dps to cover for a tank's bad threat generation. It's just more noticeable. Plus, even in fights where there is no real risk of you dying, threat generation can still matter.

Q u o t e:
1) Mindlessly stack stamina and/or bonus armor at the expense of all other stats
2) Move out of the AoE damage when you're supposed to (just like healers and DPS)
3) Use your personal cooldowns when your boss mod says it's time to
4) Pray the healers remember to use their cooldowns when it's their turn, and that not too many will have to move at the same time or (worse) die because they didn't move when they were supposed to

I think #3 is more of a big deal than you give it credit for. While there are some encounters with a big, predictable burst coming, not every fight is like that. Plus, tanks have more than one cooldown and deciding which to use when can matter. If you waste a big cooldown when you don't need it, then you won't have it for the next time around.