Americans seem to want to believe that they speak English, and we speak British English in England (meaning Britain!). They are wrong. They speak a dialect of our language, called American-English, an offshoot from the main trunk if you will, which has evolved somewhat independently of English. American-English is an out and out dialect of English. How can English English be a dialect of English?
I presume you are referring to the dialect of the ruling classes.
American pronunciation is definitely more similar to 17th century English than British RP.