I've also seen campers without chocks. Also once a 5er (right beside us), when unhitiching, slid down hill and slammed into the bed of the truck. Bent the sides pretty bad. The U-shaped tail gate he had attached stopped the camper from sliding on down into the trees behind it. He did not chock. So simple.
Our PUP, one time, I set up camp on a slight hill, but it rained and everything was wet. No chocks. Although all the stablizer supports were down, the entire camper started sliding! YIKES... It slid about 3 feet and stopped. Luckly, I did not have the awning out, or it would have ripped it from the PUP. That's when I started using chocks, even on level ground.
Yea, chocks are so simple, even a log of firewood is better than nothing, yet so many do not do it.
I also chock at home in my driveway. Winds are pretty strong where I live, but the camper has never moved. I attribute that to the chocks.