A 5-foot wingspan on a quad allows for huge props. That can lead to very long flight times with a well-engineered drone.
My 3DRobotics Y6 can do 90km/h, even if only for 8 minutes on one battery. That's a range of 6km, including return flight. Range would be higher at a lower speed, as it's more efficient, although I haven't had the balls to send the drone that far away from me in flight to test it. I'd guess I could do 10km out and 10km back on a $75 battery if I had the nerve to lose sight of my baby for that long.
See http://diydrones.com/profiles/... . These guys hope for a 1-hour flight time out of a quad with 27"-29" props on a 12kg (26lb.) drone. That's a range of 25km out and 25km back at a speed of 50km/h, which is not that fast. They've done some math that leads me to believe they are at least in the ballpark. And these guys are hobbyists.
Not such a stretch to think a company like Google could cover some good distance with a quadcopter of 9kg (19lbs.). 16km (10mi), as you say, is definitely achievable with current technology, and battery technology is due for a drastic improvement, with all the resources being put into it by different universities and companies.