I am, of course, pontificating based on what others have told me rather than as a result of detailed of the various editions. :)

However I have been told that words have been changed where UK usage does not tie in with US, e.g. "fringe" has been altered to "bangs".

Also I understand that British expressions (can't give an example offhand, sorry!) have been replaced by American expressions, which, I have been told, may change the meaning, or at least the emphasis.