Really, this should not be ranked so low as a helm enchant. It is, in fact, the best helm enchant for the Protection Warrior. I am hoping that it is only ranked the way it is due to it being a level 60 item, and theoretically items for level 70 should be better.
Before I decided to reroll my warrior, I used it to tank with as well. I have also managed to convince every other tank that I have mentored to obtain it as well. With all the defense on the tanking gear available, anything else is just a waste. The additional threat gained from the block value is wonderful, especially when you have to squeeze out as much threat as possible.
I am really hoping to see it outdone in Wrath, but still kind of doubtful that will happen. That's okay though, I run ZG for my tiger mount that still eludes me. Thank god I actually like ZG. ;p
The items needed can be easily obtained with a small group of friends. Three people makes it pretty painless; tank, healer and solid dps.
Broodlord Mandokir is the easier of the two bosses that drop the Primal Hakkari Idol. Then just kill the trash around the hoodoo piles and hope for a warrior doll. There are several piles around High Priestess Arlokk's temple that are easy to clear. A few others here and there along the road that are also pretty easy. Most of the trash you won't need to clear, at 70 you can dodge a good part of it if you're careful. The axe throwers are still a nuisance, but healers can range the throw and still keep you alive.