I fail to see why anyone would be shocked to see America ready to pounce on Syria. I mean the government has had a hard on for them since well before 9/11. The only thing keeping us out of North Korea is a full fledged WWIII with China, North Korea and Iran.
Right now Syria is the odd man out so the US figures why not make sure the interest that we deem as "right" is well supported and oh by the way maybe we will shut down the air space over Syria just to make sure things go our way.
Whether you think it's the right decision or the wrong decision it is going to happen.