Apple not licensing its OS to other hardware vendors, gives Apple a big advantage overall.
Anytime there is any type of hardware upgrade, Apple gets the credit (and traffic/hits/sales). When a new processor gets released by Intel (for example today’s 8-core release), Microsoft will not get any new traffic from it; However, Apple will get millions of unique hits (once they release it) because of the hardware release.
The other good part, is that Apple can guarantee that anyone that has an Apple, has a good reliable, fast, non-sluggish experience. With Microsoft, they can’t guarantee this since Windows runs on any PC hardware which is not sold by Microsoft.