PBS has not been shy in touting the ratings success of "Downton Abbey," last year declaring the series its most watched drama ever. And there’s no denying it’s a smash: Once DVR replays and online streams were tallied, Nielsen estimated 15.5 million Anglophiles watched last month’s season-four premiere. Those lofty numbers would make even execs at commercial networks go “golly,” and they also put "Downton’s" audience ahead of big hits such as CBS’s "Elementary" (14 million viewers) and ABC’s "Scandal" (12 million). It’s undeniable that the "Masterpiece" offering is one of the most successful British TV imports ever. But is it safe to call "Downton Abbey" the TV-show equivalent of the Beatles — i.e., the biggest thing ever to hit our shores from the United Kingdom? Well, that’s trickier.