"How is it that high-level Americans seem to speak less well than low level Brits?" I kept asking myself. And found no answer. After a few weeks I came to a startling conclusion. The apparent superiority of the Brits had nothing to do with either intelligence or education. It was in fact physical. If you pay attention, you will notice that the British, particularly the English, tend to form their words on their lips, while Americans form them in the throat. This phenomenon is particularly noticeable among males, whose deep, gravely voice is considered to be masculine, virile and seductive. I believe that forming words in the throat puts abnormal strain on the larynx, which is why Americans so often tend to stumble over their words. They frequently interrupt their speech with interjections such as "um", "ah", and other irritating hesitations. This is not because they don't know what to say next. It's because they are giving their vocal cords a momentary chance to recover.
via acm.org