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

[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.