isn't GA (General American) the "standard" American variety? That's what we learn here anyhow.. Though I wouldn't doubt it if someone spoke RP some places in America, since America does have pretty strong connections with Britain, language wise.
The RP English you're talking about isn't very common over here anymore. It's even pretty rare on the BBC now. It's generally reserved by the masses for job interviews and court appearances
You'll find that when you speak the Queens English (BBC English), accents start to fade. Just look at people like Kelsey Grammer, he could pass as English middle class very easily.