This was probably done at Maliki's request. Fat Boy threatened him if he met with Bush, and I think he's more concerned about Fat Boy than about Bush, unfortunately.
Didn't Maliki just meet with Ahdmadinutjob? I imagine the pressure is coming more from his friend in Iran than Fat Boy... though I don't doubt that has a play in the equation. Heaven help them if they pull something to publically embarass Bush.