One point that occurs to me:
Acura, Lexus, and Infiniti, I wouldn't say, are owned by their parent companies. I'm not exactly sure on this, but I believe that they are simply divisions of the parent companies, and not sepereate entities, as they were always a part of those parent companies, unlike some other companies which were once independent and were bought by larger manufacturers.
From a business standpoint, are they officially seperate entities? For example, can you buy stock in Acura motor corp? Or would it be, as I'm guessing, part of a share in Honda Motor Corp?