Good question and interesting take on things.
"Could it be the folks not agreeing with the next venture into another regime (Tehran) have declined to go to the party under duress?"
No, it's almost certainly not related to any foreign policy at all. There was always going to be a reshuffle at this point, Blair is looking like a total lame duck at the moment and the last couple of weeks have seen a number of embarrasing incidents, so he needed to look like he was doing something.