Yes, yes, we’ve heard it all before – that the sitcom is an endangered species. But with ratings down, no new hits, and a few high-profile franchises ready to wind up, some are beginning to worry about the sitcom as a genre. “Hit sitcoms are so lucrative to studios, which sell reruns to local stations, that they help compensate for the expensive process of developing new shows. Moreover, television has suffered a paucity of smash comedies for several years as viewers drift away for unscripted fare such as “American Idol,” “Survivor” and “The Apprentice.”