You're right on that point.
Though with regard to the 5th wheel on a tractor trailer, those have a braking system for the trailer that is much, much more reliable and the kingpins are designed with a longer pin to allow for "some" movement left to right.
Not to mention a tractor trailer 5th wheel is just plain tougher material.
Also, the brakes on a semi trailer are much more likely to stop an unhooked trailer than the rinky dink electric crap on a typical goose neck, or 5th wheel pick-up pulled trailer.
But you already know this.
I only know what I got popped for back in 2008 and no safety chains on a 5th wheel hitch was part of the short list of defects.
It wasn't imagined, nor was the fine very easy to forget.
In truth, the OP's problem actually proves the need for safety chains.
I also think he needs to look his equipment over better before he moves his truck.
2 times with the same mistake means there's a problem, figure it out before you kill someone..
Mark.