How did I miss this thread.
I agree with your point that buying practices vary widely within a company - that was certainly the case with Chrysler Financial when they were pushing dealers to get their floorplans. Often the ability to get deals bought isn't based on the talent of the Finance Manager, it's based on what dealership he/she's working at.
Concerning Ford Motor Credit, I remember in the old days they were so strong that mega-dealers would want to have a Ford store in their portfolio just so they had access to FMC. At one point FMC's largest dealer in Hawaii was a Dodge store and FMC did a great job of supporting the store even though they were selling a competitive make.