Which would you rather own, running Vista/Ubuntu/Solaris?
And, part of why OSX is so great is that the software is made to suit the hardware, unlike Windows.
Ok, but which would you prefer if you only had the choice between:
(a) beautiful aluminum iMac, running Vista
(b) ugly Dell XPS, running OS X with iLife
I choose (b) -- I choose Apple primarily for their software. The fact that their hardware looks fantastic is just gravy.
Of course, as others have said, there's no clear-cut division, and the fact that the software is so preferable is, like you say, a function of the hardware being designed specifically for it (and vice versa).