Well you corrected yourself there. if a Class was intended to use only PLATE then Blizzard would not have allowed them to use other gear. Blizzard decided however that they wanted to encourage classes to use more of a specific gear, so no a DPS warrior might have to chose between a Mail piece with better stats or a gear specialization. Again if Blizzard only intended a class to use a specific gear, they would only allow that class to equip that specific gear. I guarantee you there will be pieces out there that will temp Plate wearers away from all Plate or Cloth caster pieces that temp druids/shammies.
What you can't stand doesn't matter if the BIS is not a classes ideal armor type.