From Alex Massie's blog at the Spectator:

[randomness]

What We Say vs What We Mean vs What They Understand:
(achinhibitor's comment reminded me of this.)

Comments

[r-ness.livejournal.com]

I think the chart uses the EU for "others", and means people who don't understand English well enough to know that the literal translation isn't what's meant.

You're clearly familiar enough with the British to know what they really mean. :)

[achinhibitor.livejournal.com]

Part of it is that US culture, particularly urban, educated culture, uses the British forms as a formal ("high register") variety, especially when there is a relationship of formal authority which one is avoiding invoking.