Earlier quoted context omitted.
Why then in other markets are there multiple premium brands? Say for example cars, Lamborghini, Ferrari, Porsche... There is no Apple in that market. Or take watches as another example, so much choice. Apple is the only company that has nailed the premium computer. Why?
I don't agree that there aren't multiple premium brands within the phone, computer, and media player spaces, but humoring you, I would say that platform lock-in is a factor. If I sell my Ferrari to buy a Lambo, I don't have to find new gas stations and roads to use.
I think you're right that platform lock-in is one factor. I think the other factor is that Apple uses their own proprietary operating system. They have control all the way down to the hardware level and that gives them an advantage. When I close a MacBook it goes to sleep. When I close a premium Windows laptop there is a fairly high chance it's going to overheat in my bag. This is of course an issue that can be fixed but its only one of many smaller things that make up the whole product. Because Apple consistently gets enough of them right people look past the smaller flaws and see a polished product in a way that is not often seen in consumer electronics.