It Just Isn’t Done

Why do you suppose Obama bowed to King Abdullah? The implications are rather frightening since no other leaders bowed to anyone during the G20 meeting. Why show obeisance to him, but not say to the Queen of England, the official hostess of the event?
In general, heads of state do not bow and scrape to other heads of states. Since its founding, American Presidents have emphatically refused to do so. Please, somebody buy a copy of Miss Manners to keep in Air Force One.