I'm not at all sure that there is a "standard" American way to pronounce the language, although Midwestern flat is probably the one most often heard in the media (except for evening television shows that use an objectionable California dialect that is rapidly spreading to everyone under the age of 22). I have been told that "standard" British pronunciation derives from the English public (which to us means private) school system. I'm reminded of a story that my mother tells. She claims that she thought my father's first name was Otto until she saw it on their marriage license. His given name, like mine, is Arthur and his cognomen is also Art. However, since he is from Providence (Rhode Island), he pronounced Art as "Aht". Go figure. We also have towns in the US called Cairo (kay'-ro), Pierre (peer), Berlin (ber'-lin) and Prescott (pres-kit).