Perhaps this explains (at least partially) the fervor of some airport operating authorities and airport police units in patrolling the airport's perimeter (the only thing they can "control" juristiction-wise), even though the threat envelope created by the missles extends much further out. Since these missiles could easily and quickly be pulled out of a car trunk and fired, one can see why the airport folks are leaning towards making the airport perimeter an exclusion zone, and just trying to keep -everyone- (including spotters) away. Even though the threat area is huge, the airport folks don't (understandably) want it happening from the area that they're responsible for.
The US Congresscritter quoted has a good point as far as the estimated $10 billion cost to outfit the domestic fleet with countermeasures, i.e. that a successful missile attack (absent countermeasures) could quickly create $10 billion in losses (and more) via an economic shutdown.