Yakov A. Jerkov

Вот про Standard American English из Википедии: http://en.wikipedia.org/wiki/General_American

General American, like British Received Pronunciation (RP) and most standard language varieties of many other societies, has never been the accent of the entire nation. However, it has become widely spoken in many American films, TV series, national news, commercial ads, and American radio broadcasts.[citation needed]

The General American accent is most closely related to a generalized Midwestern accent and is spoken particularly by many newscasters. It is thought to have evolved from the English spoken by colonials in the Mid-Atlantic states, evolved and moved west. Walter Cronkite is a good example of a broadcaster using this accent.[citation needed] This has led the accent to sometimes be referred to as a "newscaster accent" or "television English". General American is sometimes promoted as preferable to other regional accents.[citation needed] In the United States, classes promising "accent reduction","accent modification" and "accent neutralization" generally attempt to teach speech patterns similar to this accent. The well-known television journalist Linda Ellerbee, who worked hard early in her career to eliminate a Texas accent, stated, "in television you are not supposed to sound like you're from anywhere";[1] political comedian Stephen Colbert worked hard as a child to reduce his South Carolina accent because of the common portrayal of Southerners as stupid on American television.[2][3] General American is also the accent typically taught to people learning English as a second language in the United States, as well as outside the country to anyone who wishes to learn "American English". In much of Asia and some other places ESL teachers are strongly encouraged to teach American English no matter their own origins or accents.

И вот еще ссылка. Там пишут, что на стандартном американском толком ни в одном регионе не говорят, но на нем специально учатся говорить: http://www.pbs.org/speak/seatosea/standardamerican/