Unlike Tankadins who can reach 102.4% Miss+Dodge+Parry+Br, Br+BV is not yet a mitigation stat for warriors. Its a mix of both mitigation and avoidance (avoidigation!!) but without the reliability of mitigation or the damage reduction of avoidance.
So, for what you call a "Boss set", warriors tend to avoid Br+Bv for more EH (sta, AC, ...) or more avoidance.
On Bosses, expertise/hit is more profitable for DPS/threat than BV.