@Grak
You're is actually kind of right. Half the reason EH has become so popular is the last two raids (ToTC especially) have thrown out a lot of mechanics that avoidance can't save you from, and that is no fault of the players and all of the design team. It's so much purely magic damage as it is unavoidable damage, like Gormak's impales or a Jaraxxus fireball or a Twin's orb or Anub's frozen slash. Sadly no amount of avoidance, even if stacked correctly, can dodge Anub's frozen slash, and so a tank needs enough EH to be able to take that without dying.

I don't like it, at all, but its not really the tanks fault, and my guild does TotGC with a warrior/DK tanks and we have no problems.

And remember, the point of avoidance is (in most normal fights) to avoid not every hit, but to avoid a string of hits, which is often the main reason for a tank going down. The more avoidance you have, the higher the chance you won't get hit TWICE in a row, and even less so three times in a row, and even less so four times in a row.