Umm, in some places in Alaska, there's really no feasible way to travel interstate without an airplane.

Also, it's worth considering the end result of the kind of reasoning you gave. Do you contend that the US government has the right to put restrictions on interstate travel by car, bus, train, plane, and every method of travel other than walking, leaving walking the only legal method of interstate travel? That sounds like an absurd situation, but it is the logical end result of the reasoning you've given. Sadly, when the DOJ was asked a question along these lines in the Gilmore case, they took the position that Gilmore could hire a chaffeur or something to drive him interstate, therefore his right to interstate travel hadn't been infringed (if I recall correctly). I think that's wrong-headed.