There is nothing intrinsic about being in national airspace that would confer citizenship on a child born in an airplane, either. For instance, if it were an Air France flight, the interior of the aircraft would be French territory. The woman wouldn't enter the US until she landed there and cleared customs.
So it is the Landing that would confer citizenship? What is the child before landing? In limbo?
This argument dovetails with the Abortion argument. There are those who are fond of legal technicalities that argue a child doesn't exist as a person till it exits it's mother. How do Freepers feel about THAT argument. I dare say most won't agree with it in regards to personhood, are fine with advocating it for citizenship.