“Paradoxically, a format that hasn’t changed since Mr. Carson codified it (monologue, celebrity, musical guest), is ideally constituted for the cut-and-paste ethos of YouTube and Twitter. Far more than a drama or a reality show, a joke or musical number can be plucked and posted online as a stand-alone. There is no need to DVR: Why record the cow when the Internet and social media can give viewers the milk free?”