This is the case for the amount of armor rating (and therefore damage reduction) that a piece contributes to your total. So, an armoring with a rating of 66 will translate into x armor rating for head/chest/leggings, but something less than x for gloves and boots, and even less for belt and bracers.
Not. Armor values for waist and wrist slots are the same as for hands and feet.
At rating 74, medium armor has an armor value of 333 for head, chest and legs, and 208 for wrists, waist, hands, and feet.