Air isn't the only way to deliver. You are thinking conventionally, which is understandable since you're not a psychopath as far as I can tell. However, you are not thinking low-tech enough. That's a big problem with trying to anticipate and preempt an enemy of this type: when all is said and done, they are a primitive culture, and on top of THAT, they are NOT Western. No matter how Westernized Iraq might become, they will never - CAN never - BE Western. They think differently, and every act of war is steeped in magic. I know it's hard to believe, but it's how these people think.
I'm not impressed with how they think. They've invented nothing and contributed nothing to society or technology for centuries. Magic won't win wars or even battles for them, either. If they can't control their own skies, then they can't control ours, and the air is the best way to aerosol-dispurse chemical attacks. All other methods are innefficient.