Another attractive way of applying the surfaces in a shower is to apply cement board right over the MR drywall. On this, tile or stone is set. The effect is to have a thick tile on the wall, and the backerboard is concealed by applying a 1" tile edge or border over the backerboard and tile.
Its just a means of getting a solid shower in without worrying about the transition of materials, and allows for better waterproofing.