Is there a clear line between 1 Ton and 3/4 Ton?

What about Ford who will put a bigger cab or bed on the truck and bump up the GVWR so the payload is close to the lighter version of the same truck? All the rest of the components are same.

The same F250 from 2005 can have 9600-10,000 GVWR just because you chose a different cab. If you chose the F350, if could range 10,000-11,500 lbs based on cab selection.