In a domestic mailing list for CW lovers I belong to, it was questioned by a member why we often put "San" after names. Some foreign hams do the same way. On the other hand, in western countries, they won't add Mr. or Mrs. etc, which might be equivalent to San to their names in the QSOs.
It expresses, I believe, an aspect of the difference of cultures on each side. "San" is a polite and courteous term being often used when we call someone in real conversation. Unlike Mr. or Mrs. in English, however, it won't mean a formal relationship. We are scarcely conscious of the formality with the word "San". It sounds fairly friendly as well. When we call the other with San, the reltionship is not very close but in a kind of intimacy. This word means the distance from the others as well as the warm attitude toward the others.
Our culture is composed of fairly monotonous or homogenous culture, even though there are a number of cultures of the minorities. It is assumed, as a kind of common sense, that everyone feels or thinks on something in the same way. Or, maybe, I should say the background of such way of feeling or thinking is believed to be shared by all of us. Globalisation and transfer of goods or of people across the borders have made it undergo a drastic change now. But this culture with a historical backgrpund still seems to determine how we feel or act for someone else in our country. We won't stop using San for somttime.
In the western country, on the other hand, there are people with different racial, cultural or religious background. Or such people are facing each other across the borders. In such a situation, it might be necessary for them to express their friendliness toward the other by some action. In heterogenous societies, it might always be necessary for them to overcome the difference. Shaking hands, hugging and so forth. Calling someone without formal prefixes like Mr. or Mrs. etc. is not an exception.
It is interesting that apparently trivial manner of QSO is still determined by some culturral thing.