Question on Reese Hitch Rails? 10 bolt versus 4 bolt

The 5 bolt Reese rails that I purchased were specified for the frame brackets that are turned out towards the tires. In other words they are longer than standard rails and a little thicker than the standard Reese rails in my other truck. I compared them side by side and the difference was obvious. I am not sure what additional strength is obtained with the center bolt as it only attaches to the truck bed, where as the outer bolts are attached through the frame brackets.