this is inevitable (from a technology perspective), you only have to look at the leaps in the technology over the last couple of years in drones, FPV and RC technology to see its a very valid future form of business.
The only thing that will stop it is regulation. But this will soon change as the benefits and costs are weighed up, for example reduced short distance road traffic, which contributes most to congestion.
In terms of the silly things like not being in, well, clearly you didnt read the article, its designed for 30 minute delivery. I think if you have paid for such a service, you will be there!
Battery swap stations could be set on elevated platforms, perhaps above electricity pilons/mobile substations for example to allow longer deliveries if battery technology does not improve at its recent rate.
There are few technological barriers to implementation.
You could be sent an SMS when the drone is nearby, and it would require a confirmation text to do final delivery. Delivery points could be elevated, or accessable from higher floors only.
If you think this will not happed, you are mad
Drones are very powerfull, and with clever control systems they can fly with as little as 2 of 4 motors for example.
Check these videos out (and these are old!):
http://www.youtube.com/watch?v=UQzuL60V9ng
http://www.ted.com/talks/raffaello_d_andrea_the_astounding_athletic_power_of_quadcopters.html
Imagine teams of smaller quadrocopters working as a unit to deliver larger items, working through small spaces, and even when damaged. Its possible, and not far away!