When big corporations have bad news to announce, they often hold off until as late as possible on a Friday afternoon. By burying the story over the weekend, they hope to minimize criticism from the press and outcry from the public. That no doubt figured into the timing of Infinity Broadcasting, which waited until 4 p.m. Friday to blow up two of its heritage oldies stations -- WJMK-FM (104.3) in Chicago and WCBS-FM in New York. With absolutely no warning, their popular and successful formats were replaced with a trendy pop/rock hybrid known as "Jack FM." Make no mistake about...