en.wikipedia.org/wiki/Indian_English

Use of the English words 'uncle' and 'aunty' as suffixes when addressing people such as distant relatives, neighbours, acquaintances, even total strangers (like shopkeepers) who are significantly older than oneself. E.g., "Hello, Swathi aunty!" In fact, in Indian culture, children or teenagers addressing their friends' parents as Mr Patel or Mrs Patel (etc.) is rare and may even be considered unacceptable or offensive (in the sense of referring to an elder person by name). A substitution of Sir/Ma'am, while common for addressing teachers/professors or any person in an official position, would be considered too formal to address parents of friends or any other unrelated (but known) elder persons. On the contrary, if the person is related, he/she will usually be addressed with the name of the relation in the vernacular Indian language, even while conversing in English.[citation needed] For example, if a woman is one's mother's sister, she would not be addressed (by a Hindi speaker) as "auntie" but as Mausi (Hindi: मौसी) (by a Kannada speaker as Chikkamma Kannada: ಅತ್ತೆ). Calling one's friends' parents aunty and uncle was also very common in Great Britain in the 1960s and 70s but is much rarer today. The terms 'Uncle' and 'Aunty' with certain intonations can also connote a derogatory reference to the advanced age of an individual.

also an interesting read - and read the comments!:
http://www.indiacurrents.com/articles/2010/01/06/please-dont...

http://en.wikipedia.org/wiki/Etiquette_in_Asia
Older people are rarely referred to by first names; they are addressed with such honorifics as Mr. and Mrs. or the appropriate non-English equivalents. Sometimes terms such as "Uncle" or "Auntie" are appropriate for older non-relatives.