Some people think that Bin Laden is still alive. While the US government has certain credibility issues, a little common sense would go a long way into understanding why they wouldn't lie about this.
If Bin Laden is alive, I would think that he would be motivated to put out another video in order to embarrass his foes. For him to stay silent and "play dead", you would have to think that it is in both Bin Laden's interests and the US government's interests to mislead everyone else into thinking that he is dead.
Truth may be the first casualty of war, and it can be argued that some lying is needed when the enemy has access to the same Internet as everyone else. But a skilled liar has to tell the truth occasionally in order to keep his lies believable. Whatever you think of this war or the current president, there is no doubt that Bin Laden is dead.