They have the exact same disincentive to attack our military as always. AFAIK, we never made attacking our forces a war crime, punishable by imprisonment beyond the end of hostilities. And the world and the democrats are not going to let us start in Iraq.
So why issue the statement if all its doing is re-affirming that we can't prosecute them for war crimes? By the way, I doubt one in a hundred people fighting us right now care either way.