There was a time when, if a musical was a smash hit on London’s West End, it was soon to be a similar hit on Broadway, and no one bothered asking whether the action and staging would “translate” well to an American audience. But increasingly, the biggest hits in London are falling flat in America’s leading theatre cities. Part of the problem is simply the London audience’s affection for a specific style of theatre from which American audiences long ago moved on. But the larger issue may be the incredible specificity of recent London productions: shows which require an offhand knowledge of recent UK political and social history are likely to meet with blank stares across the pond.