Chris,
I'm guessing trailer lighting laws vary across states.
I don't know where the photo was taken, but the F-150 guy would be legal in NC (I think).
On every trailer, semi trailer or pole trailer weighing 4,000 pounds
gross or less:
(a) On the rear, two (2) reflectors, one (1) on each side. If any
trailer or semi trailer is so loaded or is of such dimensions as
to obscure the stop light on the towing vehicle, then such
vehicle shall also be equipped with one (1) stop light.
http://www.ncdot.org/dmv/vehicle_services/emissioninspection/regulationsmanual/download/CR435NCDOTEnforcement.pdf
Steve
Edit. I just caught the fact that the law doesn't say anything about whether the trailer's stop light has to work.