In fact, this is a very real concern. Recall this recent news:
http://www.cnn.com/2009/US/12/17/drone.video.hacked/index.html"
They stopped using the encryption because it wasn't feasible for their operation. The issue is that even if they make it feasible, you are still open to a variety of electronic attacks against your base of operation, your communication network, or any place in between. It is argueably easier to shut down a U.S. military communication channel than it is to shoot down one of it's fighter planes.
If Shiite militants can figure out how to intercept U.S. military feeds, imagine what full fledged military and intelligence agencies can do (think: China, Russia).
You can argue that, well, they should have used encryption, but the fact is they weren't, and this was during a wartime military operation. The point is that there are numerous holes in the system, some known, some not, and it is a very real concern. Your predators on the other side of the world are about useless if your communication satellites are shot down or disrupted.