...The latest casualty turned up last week. WHFS-FM, the "alternative" station that pioneered free-form rock radio in Washington in the 1960s and '70s, abruptly pulled the plug on rock and began carrying Spanish-language pop. The move by WHFS's owner, Infinity Broadcasting, left the Washington region -- a radio market of more than 4 million people -- with just one area-wide station, DC-101 (WWDC-FM), playing contemporary rock. In economic terms, the move made perfect sense. So-called urban -- black-oriented R&B hits and hip-hop -- and ethnic formats have been the radio industry's growth engine. Among these, Spanish-language programming has been the...