NBC, the peacock network, should get a full-scale preening at the hands of its new entertainment chief once the Comcast Corp. takeover is complete. Comcast has said that it's appointing Bob Greenblatt, the programming executive who transformed Showtime into a pay TV powerhouse, to head NBC Entertainment. Bob Greenblatt Comcast on Tuesday gained approval for the $13.8 billion acquisition of NBC's parent company, NBC Universal, from the Federal Communications Commission and Justice Department. Exactly what Greenblatt will do is unclear, but he's a widely respected programmer in Hollywood, known for taking risks that pay off. At Showtime, he shepherded onto TV hit shows such as "The Tudors," "Dexter" and "Weeds," all of which have gone on for multiple seasons. NBC, the fourth-ranked broadcaster, has only recently lived through the debacle in which it put host Jay Leno's talk show on at 10 p.m. on weeknights, and replaced five hours a...