Have you ever wondered, "Why Do Americans and Brits Have Different Accents?"
Well, in case you ever do wonder, here's the answer for you:
In 1776, whether you were declaring America independent from the crown or swearing your loyalty to King George III, your pronunciation would have been much the same. At that time, American and British accents hadn't yet diverged. What's surprising, though, is that Hollywood costume dramas get it all wrong: The Patriots and the Redcoats spoke with accents that were much closer to the contemporary American accent than to the Queen's English.
It is the standard British accent that has drastically changed in the past two centuries, while the typical American accent has changed only subtly.
As a Pittsburgh native, I would like to point out that one of our sacred linguistic duties - along with the eliminating the use of the verb "to be" in order to maintain the strategic US Verb Stockpile - is to combat the insidious danger of non-rhotic speech whenever possible.
Those seemingly gratuitous "r" sounds you hear from us when we talk about "warshing up", or tell you that something is "old fasherned"? Yep - that's the noble citizens of da 'burgh, protecting yinz fellers from that there non-rhotic English n'at.
Thankfully, we do not have to stand alone in this task. Our brethren in the Auld Country are also doing their part to fight the scourge of non-rhotic speech:
The lofty manner of speech developed by these specialists gradually became standardized — it is officially called "Received Pronunciation" — and it spread across Britain. However, people in the north of England, Scotland and Ireland have largely maintained their traditional rhotic accents.
 Thusly: while the majority of the country would squander precious verbs, saying things like "the porch needs to be painted", your noble Pittsburgh brethren would simply point out that "the porch needs painted". This allows the US to stockpile these verbs so that the State Department always has a large quantity available for writing strongly-worded, yet oddly ineffective, diplomatic notes.