I believe by 'conventional' they meant 'non-braked' trailer. When the tow vehicle is stopping the trailer, the rear of the coupler is pushing on the ball.
As for the magintude of the force being less, I beg to differ. Unless they have some numbers to back that statement up (which I doubt) it's called an opinion. In my opinion, the force could be very similar. A 3000lb trailer being braked by the tow vehicle at 1g will exert 3000lbs on the 'rear' of the ball. I thought somebody somewhere estimated the chain tension to be in the neighborhood of 2000lbs per chain on the Andersen system IIRC... At any rate, a key difference is that in a 'conventional' or non-braked trailer, that pressure is only in that direction when braking (or when the trailer is pushing the vehicle downhill). On a trailer using an Andersen setup, that pressure is there virtually ALL THE TIME. That's where I've got a problem... Unless they have worked with the coupler manufacturers and dones some long term testing of a variety of couplers for compatibility (which I'm not convinced they did), I would take their claims with a grain of salt.