To me the quoted article seems to be "sour grapes". Of course Mac OS X is different from Linux or IRIX or AIX, but on the other hand, IRIX is different from AIX and Linux also. I all depends on your definition of Unix. If you define Unix to be strictly your favorite Unix-like system, you exclude all the other systems. If you use a loose definion, you can argue that Windows is a Unix system, because you can run quite a few Unix-based packages under Windows.

I think Mac OS X is Unix, because I can work on a Unix command line, using typical Unix scripting, and even use the same /bin/tcsh initialization files as on IRIX, AIX, and Linux (with a few switch commands to take care of the different flavours of Unix). I can run GNOME or KDE on my iBook under OS X, if I wish, or I can use the Aqua user interface, if I want (and I do!). I don't think you should be too restrictive about Unix. It is more about the mindset of organizing things than the user interface.

A lot of OS X is Unix-like, some of it is not. You should remember that the Unix system was developed by the geeks for the geeks. If you want a Unix system to be usable by the general population, you have to make a new environment for them to use. This Apple has managed, while preserving the power of Unix underneath. Perhaps the writer is terrified of the fact that non-geeks can actually use a Unix system without having the Unix mindset?