If you take a large company like Sony, LG, or Panasonic (or some similar company), they have many product lines. They supply to some companies that are competitors in some of their product lines. The competitors buy from them because it makes sense to do so rather than spend the money to develop a similar product. As Tesla creates more product lines it will make sense for competitors to use their electrical services to enhance their own vehicles. In other words, as Tesla becomes a company that has many product lines, the idea that it is only a car company will diminish and Superchargers will be seen as an electrical service rather than as a competing car company.