You lot (Americans) also refer to strangers with a respectful "Sir" or "Ma'm". You also use Mr. where we'd simply use the surname.

There may be other examples..

Does anyone know how come the British are generally more informal when referring to others (bar specifically those with Knighthoods or medical Dr.s or University Profs), and why the US are more formal?
Where does this cultural difference come from?

I think it may come from being brought up properly and the application of good manners and civil behaviour, all things that unfortunately disappeared from the United Kingdom a long time ago.