A friend posted this:
http://www.nicholasjohnpatrick.com/post/767354896/did-americans-in-1776-have-british-accents

I don't know much about it, but there are divergences in
British accents too, are there not? Cockney, Liverpudlian,
Northumbrian. US has Boston, Texan, Southern, etc.

You want oversimplification, defining an accent by whether it's rhotic or not is an oversimplification.

is that a main basis of accents? rhotic or non-rhotic? Until you brought that up recently when I was asking about pronunciation markings/sounds I didn't even know there was a name for the 'put in/take out an R' thing. Seems like more than just 'R' is affected in accents.

The blog post doesn't do justice to the source it lists.

http://books.google.com/books?id=ia5tHVt...epage&q&f=false

While I haven't read it all, I'm not sure it entirely agrees with the other reference, a wiki page:
http://en.wikipedia.org/wiki/Rhotic_and_non-rhotic_accents

is that a main basis of accents? rhotic or non-rhotic?

Nope, rhotic and non-rhotic s just one difference in accents. There are many more. Other variations are mentioned in the Wikipedia article on regional varieties of English (link).