Back in the day, a coon's age ago, on progression fights it was not at all unheard of to take a very specific spec tailored entirely to the encounter you are trying to get past. That might mean taking improved disarm, or improved taunt, or tactical mastery etc. Things you wouldn't include in a general tanking build that you would use 24/7 for everyday raiding but that enhanced your ability for that one fight. My best guess is that is what they are doing. Also, those builds look somewhat ordinary so perhaps it's nothing more than preference.