Unix workstations were built to run Unix. A Mac pro is essentially a PC. It boots through EFI and is capable of running OSX, but all of the parts of a PC are still there. The proof is that it runs Windows.
The difference looks subtle now, when every desktop computer is essentially the same. For those who lived through this, like the writer of the original article, it was blatantly obvious.
Well it's a question of artificial ontology, isn't it? I mean, it'd be awfully tough to legally define what's a "UNIX workstation" and what's a mere "PC". Plenty of UNIX workstations have run Windows in varying capacities, so that can't really be it.
I'd think to capture the "spirit" you'd start with something like "UNIX workstation: a primarily single-user computing system designed by a vendor to primarily run that same vendor's UNIX operating system, an operating system designed exclusively to be run on that vendor's computing systems and which can't easily be run on other vendors systems". That sounds a lot like the business Apple's in (and which apparently nobody else is anymore).
