As far as printed vise data goes, use it as a guide not a rule. Actual vise weights and measurements should always supersede the printed data.
The weight should have gone up some just from the vise base redesign to a universal model. Although the universal model added weight to the swivel arrangement, it was a compromise and substantially less beefy than the stationary only models. That said, I don't recall seeing any failures in any universal vise bases.
Why go to a universal vise base? You're right again, pure economics. The 1922 ad below shows Yost with their -2- castings vs. Columbian's -1- casting. As far as I know, Columbian was the Pioneer with the universal base, with everyone else eventually changing as well.
In 1976, Starrett became the last vise co. to change to the universal base. The catalog scan below shows a good example of how your vise model would change based on the swivel or not.
I may have missed the boat on getting a nice vintage sheet-metal vise on the cheap.