[nine_k]

I'd say Lithium-ion batteries, cheap and power-efficient controllers, cheap sensors (orientation, acceleration, GPS), and the quad-copter layout.

With them you can build a device which is lightweight enough to fly for tens of minutes, and can easily orient itself. This lets you control it with high-level commands. You can say "fly there, face north, stand still", something you can't usually say to a traditional helicopter.

[sopooneo]

Exactly. Everything that the global smart-phone market pushed the prices down on.

[nlh]

Great answer(s)! (To you and other repliers -- thanks everyone.)

Makes sense. Not one single big thing (i.e. AWS for web companies), but a really great example of one industry benefitting and emerging because of cost improvements and advances in a different industry.

I, for one, continue to be excited about our drone overlords.