Oh, FAA. Why do you have to ban everything fun? First convertible jumbo jets, then the Sex Blimp business, now this. Tucked away deep inside a document titled Interpretation of the Special Rule for Model Aircraft there's a chart, and on that chart is the end of Amazon's skybot-delivery plans.
The chart is on page 11, and lists those applications of "model aircraft" (what the FAA still calls drones) that are considered "Hobby or Recreation" (and hence legal) and those that are "Not Hobby or Recreation" (and hence illegal). You'll note that one of the entries under the "Not" side is
Delivering packages to people for a fee.
... and before Amazon can even yell "but, but, we offer free delivery!" there's a footnote associated with the entry that states:
If an individual offers free shipping in association with a purchase or other offer, FAA would construe the shipping to be in furtherance of a business purpose, and thus, the operation would not fall within the statutory requirement of recreation or hobby purpose.
So, yeah, at least right now drone-based delivery is boned. It's not like Amazon's drone delivery concept was free from issues or even relatively well-thought out, but now it's not going to happen at all. Unless they're just going to deliver free things to people for "hobby" purposes.
My guess is the restrictions on using drones for profit won't last too long. There's just too much potential money to be made, and as history has shown time and time again, potential money somehow always manages to find a way.