The reduced tow rating is because it is only available in the heavier trucks.The reduced HO tow rating tells the story, I bet it has issues with staying cool (for a start).
This is why tow ratings really just need to be overlooked.
Unless you can produce a reduced GCWR rating (because I have to admit, I haven't looked) it is the base weight of the truck, and the charts are scheduled due the base weight of the trim.
I rarely stop in anymore, so I am using this reply to get someone to post me a link to, or a screenshot of, the new tow charts...