Six shows are closing on Broadway in the next few weeks. “All the departures will still leave Broadway with 20 shows (21 if “Lennon,” which opens Aug. 14 at the Broadhurst, does well with critics and ticket buyers), more than usual in the summertime when it always has been the custom to see the total of legiters and musicals playing on the N.Y. boards reduced to a handful. (In years past there have been as few as 10 during the dog days of August.)”