I agree some Brits are a little pedantic re the language.
As previous poster mentioned Elizabethan/ Shakespearean / King James Bible era , probably the most glorious in our language devolpment coincided with the early settlers to Virginia and Mass. Many so called Americanism's were common here at that time.
We have by far the most important language in the world thanks to The British Empire and The USA. I agree only about 400 million speak the language as a first language ( below Spanish , Hindi and Mandarin ), but English thrashes them when it comes to global reach and second language speakers.