I don't doubt that observation one bit. However the reasoning behind it, vs what we are discussing, is I believe the modern OEM's to save wire costs, complexity, and by more effective design and attention to detail, have been able to produce a chassis/unibody that forms a nearly universal ground plane for everything electrical on the car. Our decades old cars did not have that consideration, and also suffer from a decent amount of weather induced corrosion, etc. I see an added ground directly from battery to engine as a huge preventative measure of future electrical gremlins in our old cars as we add more electrical components..