1) The 400 AGL rule comes from the idea that the FAA administers everything above that line. Below 400 feet isn't considered navigable airspace. The FAA doesn't

1) The 400 AGL rule comes from the idea that the FAA administers everything above that line. Below 400 feet isn't considered navigable airspace. The FAA doesn't specify a global minimum altitude for aircraft to fly at (in 14 CFR 91). Instead, they specify building and person/surface vehicle distances and end with the catch-all that you have to be flying high enough to be safe in the event of an engine failure. So, they're creating rules in a manner consistent with their preexisting regulations. 2) The airspace over the Hudson appears to be class E, which is controlled. By definition, only class G airspace is uncontrolled. 3) The actual plane landing on the Hudson was an airliner in the middle of an emergency. Landing on the river was certainly not part of their planned activities for the day. The pilot-in-command is allowed to deviated from the rules to the extent needed by the emergency. I'm sure the FAA is still hotly debating how drones will be treated, but it's a government organization used to old technology and moves slowly. Silicon valley will run laps around the regulations until the VCs get bored and fund something else.