Why did this happen? Television tends to flatten regional accents, of course, but how come Britain held onto its aristocratic tones, while America's slipped softly and silently away?
Well, it's true that the aristocracy, in as much as it still exists, has maintained a certain distinctive way of speaking, but it's not heard very often. David Cameron, for example, is sometimes labelled a "toff" but his accent is very different from that of Harold Macmillan or Alec Douglas-Home for instance. There's not much cut-glass around these days. You won't, for instance, find many people in British movies talking in the manner of Trevor Howard and Celia Johnson in Brief Encounter. Then again, you won't find many movies like Brief Encounter either: