If you're comparing Mac OS X to Linux, however, that argument goes out the window. There's an ease-of-use argument that could be made, but that's mainly because it's nearly impossible for J. Random User to buy a box with Linux preinstalled.
This is not completely true. I've read that some Walmart's are carrying Linspire boxes. I think the larger problem with Linux is distribution variety. There are too many variants which creates too many possible solutions for the same problem.
Windows on the other hand has a lock on the PC market. This ensures that new hardware works on Windows machines with minimal effort. In the long run, this is what user's want. The downside here, alternative developers don't always have access to information required to support hardware. I hope this changes once OS X runs on x86 based hardware.
I prefer to use Linux on my PC but my laptop requires XP to use some of it's hardware.
Cheers, Mike T.