The part they're leaving out is that it'll only be available to people who live within 15-20 miles of their warehouses. Those drones have an extremely limited range, and they have to be able to make it back as well. And as the weight of the package increases, the range decreases. So, unless you already have an Amazon warehouse in your neighborhood, you'll never see one of those drones landing on your porch.
It's a technological publicity stunt. No different than Elon Musk and that damn Hyperloop he came up with. It makes the company look good and generates some buzz in the press for a few days, which gives the stock price a quick bump. But, the technology isn't yet mature enough for it to be rolled out on a large scale yet, and probably won't be for at least the next 10-15 years.