Wrong. There is nothing preventing the National Guard from being armed with loaded weapons. That is a policy not a law. It started after Kent State and for some stupid reason just continued.
Well, in addition to common sense.
It's my feeling that deployment of the Guard in the airports was nothign more than high profile fluff to make people feel secure.
They were completely unnecessary and it truly was a clintonian display of symbolism over substance.
(Also, yes.. I think at least some did have ammunition. I seem to remember seeing a story here on one who shot himself in the bottocks while "on patrol" Imagine, these are our saviors!)