What used to be Detroit's big 3 have become pat of the worlds big 5 or 6 (and maybe less then that). Many parts and pieces are shared within each mega corporation's branches. Those major parts (picking on starters and such) may have mounting points and other minor changes from one vehicle to the next, but the over all part has the same design and probably the same world manufacturer. The minor changes are probably part of the thought process so those parts have to be bought from the car branch sales department, or their approved sales outlets. The automotive aftermarket parts companies are always fighting with the auto manufacturers to be able to sell those brand specific parts to the general public.

Its all part of the plan from the major auto companies to squeeze more money out of the people. The plan is working well for them.