Is it simply a matter of there being a finite number of facial geometries? (You'll note, perhaps, that the Toyota Avalon looks like the latest product from Ford Design.) Was it, as others have suggested, a case of intellectual property and fair play, since Ford at one time owned Aston Martin?
WSJ: 2013 Ford Fusion Hybrid Review: Passion Seizes the Family Sedan | Rumble Seat by Dan Neil