Peter Jennings, long-time anchor of ABC's World News Tonight, died yesterday. Granted, he hadn't been on the air since April because of complications stemming from his treatment for lung cancer, but his death -- along with the retirements of Tom Brokaw and Dan Rather as the news anchors of NBC and CBS respectively -- seems to me to symbolize something bigger: the demise of the nightly television news program as an institution.No, this isn't an...