Nice point.
Personally, as far-fetched as this theory may be. I see it as a way to actually gain MORE business on Ford's part. If the employees act upon this new rule, and actually do buy a Ford, that is instant business for Ford, and from it's own employees.
Now, do I agree with this new rule, fuck no. What does this really accomplish? Are people going to drive by the plant and say "Wow, everyone drives Fords at that Ford plant, maybe I should too." Probably not going to happen. I just cant grasp the impact they are trying to have, besides segregating those who choose to shop outside of their business. Most of these employees work to make a living, end of story. Not everyone has this Ford God they look up to. Some of these people probably could care less if they worked for Ford, Chevrolet, Mitsubishi, etc, if the bills are getting paid. So to force purchasing decisions on them or be punished, there has to be some legalities involved.