I have to ask -- do even they, do that? I'm of the middle-class persuasion (and possibly a twit); but my speech habits / abilities are such that I'd find it difficult to add a pronounced "r" after a long "a", here.
This stuff gets much discussed when Britons and Americans get into matters of pronunciation. It would seem that on the whole, Americans meticulously pronounce "r"s in words, while Brits don't. The people of Boston, Mass., are among the US's few non-"r"-pronouncers: their compatriots find it hilarious to imitate Bostonians saying such things as "I'll pahk my cah in Hahvahd Yahd". I have trouble imagining how otherwise, I would or could pronounce that sentence.
When I was in Miami can you imagine the confusion on the face of a barmaid when asking for a bottle of water, took a few goes until I said Waaadder then she clicked