You are right, novice users don't install operating systems, but most laptops come with one pre-installed. Not knowing any better they could simply go by aesthetics when they select computers. In this case they are likely to end up with an Apple product: the computer itself, as well as the UI, looks very good.

edit: I was a bit confused by your reply, but I now see why: I wrote 'install Windows' when perhaps should have written 'use Windows, or 'buy a computer with anything but Windows'. My mistake!