C'mon. Everyone knows the difference between "Professional Grade" GMC's and Chevys are lock washers on their fasteners...
I've heard that since I was a little kid, and it just shows you how crazy badge engineering is. Fact is, there is a significant amount of engineering in each new vehicle for safety/liability reasons (GM has 3 floors of their HQ locked down with legal files) and it gives the marketing folks something else to trump up.