The google car is an exception where there is a lot of sophisticated software. UAV's like Boeing's and even the ones you buy online (with the open source software) are running on boards, not full-scale PC's with the ability to play a DVD.
UAVs are very complicated in terms of technology and engineering, but the hardware is simple because it's basically just running control loops on some board.
No modern UAV has hardware capable of running an entire Windows installation. Think of arduino boards; those things can control huge robotics systems and they are very simple (and thus simple to debug). If you're designing a robot from the ground-up, why would you scale all the way to Windows? No one is going to be playing minesweeper inside the plane
I would think about this for a second; the DoD doesn't manufacture, produce, or design these systems. They contract that out. Considering that General Atomics Aeronautical is a smaller defense company (relative to other ones), I'm sure they could make their own decision about what OS to run on the planes and on the ground. That's all I can say...
It's tempting to say this to avoid getting your hopes up, but there has been solid concrete progress in fusion technology over the last decade. Getting net positive fusion to occur on Earth is an _incredibly_ difficult technical challenge. It's like climbing a scientific mountain, and right now we are a few hundred meters from the top with a few more obstacles to go. So saying you won't believe it until we reach the summit discredits all the progress we have made to date.
This technology is not a matter of 'is it possible?' but 'is it technically feasible?' And the scientific community has been chipping away at the latter for a long time.
UAVs are very complicated in terms of technology and engineering, but the hardware is simple because it's basically just running control loops on some board.