The MacOS X server discussion here two weeks ago included a comment from someone pushing the Linux/Unix distinction, my response pointing out that Linux is Unix and that people changing from something like HP-UX to Linux are changing Unix suppliers rather than OS architectures, and this response from Anton Philidor:
They're also changing costs.
Exchanging ( ;-) ) Unix servers for less expensive devices is a way to save money. And the differences between the operating systems can affect the staffing requirements. That can have an impact on employment, current and prospective.
The "nonsense" is arguably a significant change in the way IT operates.
What Anton relies on to make his point here is first the assumption that Linux is somehow not Unix and, more importantly his expectation that people will unthinkingly accept the implied comparison between today's costs for x86 servers and those from ten or more years ago for proprietary RISC servers.
It's true that today's Sun UltraSPARC T2 based 5220 running Linux easily outperforms Solaris on an UltraSPARC 4500 from 1997 and does so for less than ten cents on the original dollar - but this has nothing to do with any imagined Linux/Unix distinction and everything to do with the operation of Moore's law and the market.
Compare the cost of Linux or Solaris on a 200Mhz Pentium Pro in mid 1996 and there's no significant difference - just as the differences on its Xeon and Opteron successors now marginally favor Solaris but are fundamentally insignificant - particularly relative to the real gains both offer over Windows.
Look at operating costs and functionality, furthermore, and you can see that Linux and Solaris, on similar hardware, do similar things at similar costs - largely because most of the more widely used applications or application toolsets are freely available on both. Again, it's those applications, not the OS, that matter to users and it's the applications, not the OS, that offer the biggest cost and productivity gains relative to Microsoft's proprietary product set.
Notice that I'm not saying that Solaris and Linux don't have differences - Solaris includes numerous technical and administrative tools and capabilities like ZFS, DTrace, and SMF that are simply not there yet on Linux, while the typical Linux distribution includes lots of hobbyist tools, like multiple mp3 players, that aren't usually included with Solaris. What I am saying is that Linux and Solaris are divergent members of the same family, and when deployed for similar purposes on similar gear offer comparable cost advantages over Microsoft's product set.
What's going on is that moving between Unix variants like Solaris and Linux is fairly easy, but comments like Anton's reflect Microsoft's success in piggy-backing a general anti-Unix message on Red Hat's anti-Sun sales strategy - and that's the bottom line: for Anton this whole Unix/Linux distinction is probably just a mistake, for Microsoft it's a deliberate and dishonest marketing ploy, and for you it's a mind trap to avoid.