There's a good example of this in my South Philadelphia neighborhood: The Italian-Americans here speak Italian with the accent of a southern Italian from a century ago, frozen in time. Italian accents have progressed in Italy over that time, but not among the immigrant communities here.
I've read articles claiming the American accent is closer to what the British sounded like at the founding of the United States than what they sound like now.
Things like the spelling of cheque are prime examples of this. We mock the Americans for their simplistic spelling, but in actuality we took "cheque" after America had split off already in an attempt to sound more French and eloquent. American drawl accent is also closer to older English than lots of modern English accents.
