Walter Cronkite and CNN anchor Aaron Brown are the latest TV journalists to agree to appear on public TV stations in infomercials paid for by manufacturers. The New York Times put the spotlight on American Review and other series of shorts produced for a fee by WJMK Inc. of Boca Raton, Fla. Also featured was Healthology, a series of modules produced in Manhattan. The economics are similar to that of shorts World Business Review and Spotlight On and the series Visionaries, described in Current last year.