But Bush did tell us why we invaded Iraq: "He tried to kill my dad." Before he was even elected he indicated a desire to invade Iraq because he saw it as the hight of his father's presidency left unfinished. "If I have a chance to invade, if I had that much capital, I'm not going to waste it," he said on the campaign trail. He never once stuck to the WMD story; it was just what they made Powell say in public as a cover for all the other reasons he gave (see the Downing Street Memo for more details.)

If Osama had came out with a multitude of mutually-contradictory statements we'd have reason to doubt him, but he was amazingly consistent from when the CIA started funding him until the US military gunned him down.