It's non-zero, but essentially right next to zero, the number of people buying Macs who do not at all run OS X. So yes, it's bought as a whole, people want the product experience, the integration of hardware and software. That's why they buy it. If they really didn't care about OS X, or really didn't care (a lot) about industrial design they'd buy something else. And on industrial design, Dell's XPS 13 is neck and neck (bit better in some spots and not as good in others) with the Air.