Factory Specs on Tire Pressure?

.........I went to tire school put on by Good Year.......i asked the rep y the factorys has 2 different pressures, i had always assumed that because i had a ram 2500 diesel that it was ment for the payload......he said i was only partly right as the different rear pressure was for when the truck was driving down the road pushing the wind it evens out the weight distribution so theoratically there is more weight on the rear than the front.......i told him i cant really see it that way......i hope i explained it right......kim........