Precisely, and the whole reason that they even bother diagramming and dichotomizing languages and accents to begin with is merely to trace back their relative history to each other. English is complex, and even moreso because it's spoken by so many people across the globe. But when you're looking at English in a macroscopic perspective, for instance, how it evolved from German or what influence it picked up from Latin, it helps to lump all of the accents spoken across the US into one tiny bubble so that you can look at the bigger picture over time.

There are courses and whole books dedicated to nothing else but American English, to say it's vast and varied is an understatement.

If you want an example of what I mean, however, check out this book sometime. It's fascinating.

http://www.amazon.com/exec/obidos/tg...books&n=507846

A whole dictionary dedicated to nothing else but "proper" pronunciation of American English. :) It seems silly at first but sometimes it really takes things and puts them into perspective, you can really gauge how much English changes on an almost daily basis... ahh the beauty of language :)

-Nah-