Al Qaeda in Iraq probably wants to hang on till at least the day Bush leaves office hoping a Democrat gets in and declares failure the first day and packs the troops up and go home. The Al Qaeda would be free to do what ever they wanted and that would give them a BUNCH of mojo.
Let the Kurds ethnically cleanse Mosul of Sunni Arabs and there will cease to be an Al Qaeda problem in Mosul.
It is not because Al Masri is less brutal, it is because Al Qaeda has been utterly defeated and their capabilities to launch massive carnage has been greatly reduced. They will do it if they can, and they may succeed in doing it from time to time but it is much less frequent than before because they have been crushed by our US military.