OSX is one of Steve Jobs' least-discussed successes. The original Mac, Pixar, the iPod, the iPhone are all talked about -- but without OSX as a Unix-based OS, application-development on Macs, and adoption of Macs in the '00s would have been much slower and more sparse.
The distinction is important IMO, because I beleave part of the ease of them supporting multiple platforms so easily is because it was all built around a microkernel.
Now Apple has more of a hybrid with XNU, but many of the core concepts of Mach are still there.