I love my TiBook. And I love my luxo-iMac. Why? Because apple have realized what's missing in both the proprietary and OpenSource OSes: quality. Everything about the Apple machines works straight out of the box. No hours lost to configuring and twiddling messy .rc or .bat files. No scratching of heads when the old BIOS doesn't quite handle the new 3rd party hardware, or there's some mysterious IRQ conflict with some grotty jumper, or the latest RPM breaks the last 15 RPMs, or no matter how many weekends I spend on it the sonuvabitchin sound server still doesn't work, or Mandrake support flips me the bird because they decided my problem doesn't qualify, or the sonuvabitchin Windows Registry corrupts AGAIN. I don't have to rebuild kernels or fight off MalWare or wait until the next release or the release after that....
This is an appliance. And it works like an appliance. It all just works.
Now MacOsx is also a wonderful development platform. Its development tools are all free, at least in terms of dinero. But development's not why I buy these boxes/domes. What makes me shell out an extra USD $500 over the WinTel platform is MacQuality. Heck, I'd pay more than that for this.
In short, ItJustWorks.
See also: AppleAsQualityCenter