Calling nice Americans Canadians out of politeness

(Where "American" is used in the normal way to mean a US citizen, rather than a resident of the American Continent.)

An American friend of mine, now living in the UK has described how, in polite London society, she is always asked if she is a Canadian, never if she is American. She supposes that this is to avoid causing offence, rather than because she seems distinctly Canadian (she does not). There seems to be an assumption than it is less insulting (perhaps even complimentary) for an American to be mistaken for a Canadian than for a Canadian to be mistaken for an American.

I suppose that it could be that my accent sounds more American than Canadian although I have evidence to the contrary - most Americans seem to spot my Canadian accent almost immediately.

One of my favourite quotes, which supports spiregrain's thesis above, is:

Canadians are generally indistinguishable from the Americans, and the surest way of telling the two apart is to make the observation to a Canadian.

- Richard Starnes, United States journalist
quoted by Gerald Clark in Canada: The Uneasy Neighbour, 1965