Well yeah, the difference between EHP set and Unhittable is huge...

But try it in Naxxramas and you will see beoing unhittable will be something like... reduced melee damage taken by 50% or something...

With mine (as a paladin), i block about 5k in naxx... VS Patchwerk (the boss that hits harder in there).. its like having 60% reduced damage for the whole fight (if you're the top on threat of course)...

But who cares about Naxxramas at this point?? lol... At the end, being unhittable right now is just useful for a weird case (anub's adds) and just for fun in heroics; "Hey watch this, i dont see any incoming hit, all i see is Dodge,dodge,block,parry,miss,dodge,parry,block... etc.."