[panglott]

This claim is generally made less about Standard American or General American and more about regional Appalachian dialects. Even this is a myth. http://itre.cis.upenn.edu/~myl/languagelog/archives/002699.h... http://lrc.ohio.edu/lrcmedia/Streaming/lingCALL/ling270/myth...

English and American dialects both originated in (Shakespearean) Early Modern English, but both have changed over time, as languages do.

[hugh4]

To my ears an Appalachian accent doesn't sound that different to a regular American accent, it's just an exaggerated version of it.