Is actually the one about the drones. I was shocked that there were over two times the number of amateur, civilian drones flying around than military ones. I will never hack at my neighbor's overgrowing trees again... :)
I'm willing to bet that most of the drones that are counted are tiny hobby aircraft (multirotors as well as fixed wing). Most that I've seen bear little to no risk of injury should a crash happen due to light weight and small props.
Compare that to military drones that are relatively huge, made of metal, and sometimes well armed. There is a huge difference.
Alex, the statistic isn't exactly clear on that point, but I'd say with near certainty it's used mainly for prototyping. The actual data point from the element14 survey said:
"More than half (56%) of professional engineers are more likely to use open source hardware such as Arduino and BeagleBone in 2013. Among hobbyists, that figure jumps to 82%."
The high numbers seem to stem from the fact that engineers like to have access to as many resources as possible, and the open source community provides that. Strong user communities help with ease of access and use.