Read a post on another blog the other day stating that the flip arrows on elements are always on the exterior side of the element. It is definitely true for walls because they are system families, or Hosts as the current documentation calls them. If a door or window family is created using the stock templates and not altered then the statement remains true. However, the controls (flip arrows) can be moved in these families so we are depending on the family editor observing this habit. Don't think I can quite call it a standard, maybe a strong recommendation?
Ideally the flip arrows (controls) present in a family should be located so they also indicate the exterior side of a wall hosted element. Your mileage may vary!