Finally, there's a key issue about the availability of developer tools. Developing for Windows is a pain. You can find things people like less, but I've never heard of anyone claiming that Windows was pleasant or enjoyable to program for. By contrast, developing for the Mac is actually mostly pretty pleasant. It's got some quirks, but the underlying model is a developer-friendly one. The system has real documentation, and the widespread availability of good tools means that the system gets a lot of attention, and a lot of bug reports... And yes, Apple processes and works on bug reports filed by people who haven't got support contracts. Unlike Microsoft.
What this means is that developers on the Mac are having more fun, and are spending less time fighting the machine. Per hour of development, the software is consistently better. The software is more likely to have a bit of polish -- to be pleasant, rather than merely theoretically functional. And that shows, not just in the use of the base system, but in application software