And here's some more to read:
http://www.autonews.com/article/20140728/RETAIL03/307289955?template=mobile&X-IgnoreUserAgent=1
Apparently, Ford prefers to remove some various items from their lineup to prove tow ratings
Excerpt:
"A Ford spokesman insists, though, that the F-450's gross vehicle weight rating is 14,000 pounds. He explained that Ford bases its maximum payload claim not on the base curb weight, as Chrysler does, but on the weight of the base vehicle after various items are deleted from a base F-450.
Ford shaved 154 pounds from the weight of the F-450, he said, by removing items that have the possibility of being deleted from a vehicle order. Among the items removed were the spare tire, tire jack, radio and center console.
Ford said it uses this practice to set the maximum payloads for all F-series pickups.
By comparison, General Motors has based its maximum payloads on the lightest version of a pickup a customer can order from its order book, including a heavy-duty pickup without a rear bumper. That minimum curb weight is below the weight of the lightest base version.
For the 2015 model year, the weight of the spare tire will also be subtracted to calculate the lightest vehicle configuration for the light-duty pickups, a spokesman said."