Ask yourself a simple question =
As a manufacturer of UAV's would you prefer to:
(a) Make significant investments in optical recognition and collision avoidance technologies and limit the available payload that this would entail, or
(b) Prevent other aircraft from using the airspace that you're operating in (or put the cost/onus onto the manned, rather than unmanned aircraft)
More news from the BBC shows how UAV's are becoming ever more pervasive in our lives:
BBC NEWS | Science/Nature | Robot plane sweeps over UK fields