That provision was part of the Firearm Owners Protection Act of 1986, I believe.
Yep. Supported by Mr Cox's NRA, as a matter of fact! To the NRA it was a worthwhile trade-off to ban the full-autos, in order to get the federal law that allows you to transport a weapon from one place it's legal to another, even if you have to pass through a gun-ban jurisdiction.
Meanwhile, local prosecutors in Boston, Queens NY (where Laguardia is) and Albany, have started busting everybody transiting the airports there with a firearm and without a state or local license, which in those jurisdictions is made of purest unobtainium even for the residents -- let alone transients.
Thanks to Patriot Act and other post-9/11 searches, they can identify these people, and it's a lot easier and lower risk than catching actual criminals.
This flies in the face of the McClure-Volkmer FOPA of 1986, but the Bush administration is not asserting federal preemption, or doing anything to assist the people targeted by these local prosecutors (all politically ambitious Democrats -- isn't that a shock, not).
The state associations have done some things but the NRA is, somnolent... they sure did the gun owners a great deed with the 1986 law, didn't they?
d.o.l.
Criminal Number 18F