Why Didn't Richard Have a British Accent?
He did have kind of a sophisticated tone to his voice, but he didn't sound like an Englishman born and bred at all.
I read in a bio of him that he always wanted to be an American citizen and finally did become one around 1984. He was doing "Family Feud" at the time and proudly took his certificate and whatever else they give naturalized citizens onto the show to show America that he was officially an American.
Maybe for some reason, he just really dug America to the point where he not only wanted to be an American, he wanted to talk like one too.