The NWS COOP Station's are owned and setup by them. You are correct in some of those not being set up to meet their "official guidelines". One example is the Pennington gap station. It's TH Sensor is about 12 Feet from a metal building (heat source). That is way off the 30 ft away structure guideline, let alone a metal structure.
As far as the Airport problems, there are more than one. The Temp. FAA Guidelines we know are one, another is siting as well. The Lee County Airport ie is located fairly close to a Metal Hangar, thereby getting heat from it occasionally.
It is no wonder our Model's have issues and our Climate Data isn't accurate, let alone some of the less than par Observer's at some Co-op Station's.