WASHINGTON (Reuters) - President George W. Bush postponed an event on Wednesday to promote an advertising campaign on preventing prescription drug abuse after actor Heath Ledger's death from a possible drug overdose, the White House said. "We felt it would be better not to hold the event today given the tragedy of yesterday's passing of the beloved actor," White House spokeswoman Dana Perino said. "We did not want anyone to think we were trying to link into that story in any way," she said. Bush had been scheduled to talk in the morning about the Office of National Drug Control...