Joan and Melissa Rivers will find themselves all dressed up with no one to goad Sunday night. The threat of war with Iraq has led Oscar organizers to cancel the glitzy red carpet arrivals for the first time in the show's 75-year history. "To do something that will be self-serving or frivolous on a night when our troops are in bloody combat would be absolutely inappropriate," Academy President Frank Pierson said. Although the show itself is still on, Pierson conceded that "we are all at the mercy of the winds of war." ABC's pre-show, meanwhile, will now focus on Oscar's 75th anniversary.