Mac OS X is Unix. You get all the power, stability, and programmability of a Unix system. That isn't simple. It's complex. Of course most people don't have the education to use that power and complexity. But it's there under the hood for the power user. As for 3rd party software, Unix is the richest environment I know of.
With UNIX you have to compile the apps to work on your system and that’s what keeps me from jumping on Linux. It’s just too much a PITA. Windows is just too dominate to give up.
It used to be Macs had a niche market with video and photos but now windows even does it at worst on par and at best better than Mac software.