Page "Comparison of American and British English" Paragraph 5

An unofficial standard for spoken American English has also developed, as a result of mass media and geographic and social mobility, and broadly describes the English typically heard from network newscasters, commonly referred to as non-regional diction, although local newscasters tend toward more parochial forms of speech.

Despite this unofficial standard, regional variations of American English have not only persisted but have actually intensified, according to linguist William Labov.