Why is the nerf part of Frost Specialization?

Kind of seems like a slap in the face to have our Frost Specialization state that it "Increases Frost spells and Frostbolt by x, but reduces your mastery by 6". Is that supposed to make people want to spec Frost? If you are going to nerf the mastery, just do it. Don't think we need a constant reminder every time we examine the tree.