Exactly. As it has been said before, people generally do not buy Windows on its own (outside of system builders, enterprises, and the people victimized by the Vista Capable event). They get it for "free" when they get their computer from an OEM every 3-5 years (when their current computer breaks down). Of course those OEM's tend to be companies like Dell or HP (and others) that are equally as large as Apple is and sell many, many more products than Apple does. On the flip side, people keep their Apple computers for much longer and actually buy the newest versions of the OS in stores (it helps that OS X is much, much cheaper).
The fact that Apple does the kind of business that it does comparatively is amazing.