If expertise is so important, why do the vast majority of tanks with heroic LK kills on Lordaeron completely ignore it on their gear?
In just about all of the tank guides I have read, I have always seen said that after reaching the defense and hit caps that it is important to get expertise to lower the chance bosses can avoid your attacks as you are always attacking them from the front. I believe the expertise cap for ICC bosses is 26.
As far as sources of expertise, different races have +3 expertise if they are using a certain type of weapon, for example humans get +3 expertise if they are using a sword or mace. Glyphs are also a potential source of expertise as Paladins get 10 expertise while seal of vengeance is on. Talents are another source of expertise as druids get 10 expertise from primal precision. These are great pickups to gain expertise, but as the cap is 26 you need a great deal of expertise from items / gems if you want to get expertise capped as a tank.
Warmane armory has an option to see guild comps / characters that have downed bosses ranked by how long the encounter took. I have checked about 13 different tanks gears that have downed lich king on heroic difficulty and only 2 of them had expertise on any of their items (1 had Mithrios Bronzebear's Legacy and another had Grinning Skull Greatboots) while the remaining 9 had no expertise on their gear. Now all of the tanks I checked had 1 single stamina/expertise purple gem in the head slot to meet their meta requirement, but this 1 gem alone still leaves you quite short on expertise.
Again, If expertise is so important, why do the vast majority of tanks with heroic LK kills on Lordaeron completely ignore it on their gear?