My opinion – the beheading is an attempt to provoke Bush into doing something else stupid, like he did with Fallujah, and draw us even deeper into Iraq. Every penny spent and every person sent to Iraq is one less resource with which to battle al-Queda. And the more al-Queda can provoke us into seeing Iraq and Islam as the enemy, and the more they can promote tribal thinking of “us” against “them” — the better for their cause.
Bush just keeps being led by the nose by these guys. Or maybe Bush and al-Queda share a cause: war between Christians and Muslims.