LIES! OS X is NOT UNIX. It's sorta-kinda-BSD-abomination-whatever-Mach. It's arguably a lot less UNIX than Linux, which is specifically not UNIX. The only UNIXy things about it are the GNU parts, and GNU's Not UNIX.
Just for the record, I say this not as a Windows fanboi, oh no. I say this as an IRIX hardcore aficionado. Now, I will grant you that my DateTime struct is BSD. I admit that, and I apologize for it. But the rest is Bell System V Release 4, the One True Operating System; and I can ASSURE you, my friends, that OS X is emphatically NOT SVR4!
Proof? PROOF? YOU DEMAND PROOF?!
Bring up an OS X box from bare iron. Was fdisk involved? Did you need to bootstrap the thing from sash? Did your disks have slices, not partitions? Did getty enter in to your thinking? Was tar involved? Was it gtar, because THAT DOES NOT COUNT? DO YOU HAVE A FRAME BUFFER INSTALLED, YOU FILTHY HEATHEN? 19200/N/8/1?!?!?!
Nope, none of the above. Your machine goes "bonk" when you fail to enter your home zip code so that Apple can send you valuable offers of future services. If I tried to give a real UNIX box my home zip code so that I could receive valuable offers, it would probably detonate with the fury of a thousand Hiroshimas, AND the kernel would panic.
tl;dr, GTFO my ARPAnet.