This is true, Perfectlap, but we see it all the time. I just saw a Miata at work today, top down and open to the world...I won't even comment extensively on the fact that it was cloudy and foggy this morning, threatening to rain.
But yea, I doubt (and more than anything hope) that this person has nothing important in the car, because there's nothing stopping anyone from reaching in and helping themselves.
If the car's sensors are active, though, the horn will be blaring the whole time that person is helping themselves to your car's headlights as soon as they reach in to open the door(s) to get to the trunk latches.