If you mean by that bought up and owned by a volume manufacturer or with a relevance that people have to google the name to know who you're talking about: yes.

They kind of do(or did), not sure what your point is. Bently, Bugatti, Aston Martin, Porsche, etc... have all had major trouble recently. Most of the luxury brands have been bought by higher volume manufacturers.

And the car analogy still does not fly. A Bentley will work fine on the same roads a Volkswagen does. However, an iPhone will not run, say, Android apps. If Apple's marketshare drops under a certain percentage, it becomes less and less interesting to treat it as a first-class citizen.