Apparently, plot concepts that would be considered far too stale and cliched for even a hackneyed TV sitcom are thrilling audiences in London theatres this summer. Ben Brantley can’t quite explain the appeal, but he knows it’s real: “If any of these premises reared up on my television screen, I’d change the channel before the first canned snicker could be sounded. But I have to confess that I, along with hordes of other London theatergoers, experienced an almost childlike pleasure watching these crude concepts translated to the stage.”