I think it's joints that are used for moving the body parts, but not necessarily required for the transformation. For Rodimus you have the two shoulder joints, but you probably could count his ankles and neck, as his head and feet are moveable. Even if that mobility is intended for the transformation, those joints give you the option to move/pose those limbs, albeit rather limitedly.
Maybe look on the tfwiki.net to see if they have any articles on articulation or poseability.