I'm not sure what you mean by "offers." The document looks pretty official to me and certainly far more so than a rep at tirerack or a local dealer who says "uhhhh whatever we have in stock is what we recommend, I think." According to BMW CA it is official.

You can put everything down to marketing and advertising dollars, but at some point BMW is responsible for their choices in terms of safety and performance. Otherwise why not put any tire on the cars, or better yet, any size tire. For one thing people would quickly say the cars handle like crap and they're not buying BMW anymore. At the least I think 50% of any decision by a company has to do with science and perhaps 50% to marketing.