Thanks for your concern, here is what I know.
The Dana 110 axle that the F450 has in the rear is rated to 14,000lbs from Dana. Its derated to meet the 14K GVWR that Ford chose to put on the truck. That is why the payload is less than the F350 of which has the same 14K GVWR. The truck is an upgraded version of the F350 with heavier duty parts. You kind of have to read through the lines. My assumption here is that they put the low GVWR to make it easier to register the truck and get insurance on. The truck will be more truck than I currently have, I have not doubt about it.
As I said earlier, the Ram is a great truck too.