A matter of manners as well as position. If you look at letters between peers (equals) of the 18th and 19th century you will see them signed with phrases like "your humble and obediant servant" (usually abbreviated). To view the conventions of the past with the eyes of the present is always a mistake. (I don't include such conventions as impaling or "droit de signeur").
In our age of equality I find myself called to my table at a restaurant by my first name, I don't consider the restaurant employees to be my inferiors, but I'd still prefer to be called Mr. Murphy in that situation. Yet younger people seem to like the impression of familiarity - oh tempore, oh mores. Best, Jon
