I'm old, but I somehow missed seeing the BBC's most tragi-comic program: Yes, Minister, when it was new in the early eighties. The basic social situation animating the series was the conflict between the theoretical control excerised over government policy by elected officials such as the ministers responsible for each department and the real control exerted by the bureaucrats. In one memorable situation a staffer explains his betrayal of the minister's interests in favor the department's by saying something like "ministers come and go, but the Permanent Secretary is forever."
Some people I met recently reminded rather strongly of this because they made their loyalties clear: their priorities lie with Microsoft, not their employer.
It seems to come down to this: as long as there's a bull market for Microsoft skills and as long as those skills are defined and certified by Microsoft, that's who will own the people. Fundamentally it seems you can rent an MCSE, but you can't hire one within the traditional meaning of the employer-employee relationship. As far as these people are concerned, employers come and go, but Microsoft is forever.
That's not true in the Unix community. There are lots of certifiers and no single point of control through which to grab trainees so tightly that their hearts and minds must, as Richard Nixon pointed out in a different context, necessarily follow. Both Sun and Red Hat, for example, offer certification - but so do a number of organizations such as The Linux Professional Institute which are at least nominally vendor independent.
That diversity is possible mainly because Unix is Unix: becoming an expert on one product doesn't leave you captive to that vendor, it prequalifies you to work with others too. Ask your typical MCSE domain manager about PAM or pGina and he's likely to think you're making an ill advised reference to a co-worker. In contrast, ask someone with Solaris certification the same question and the core elements of the answer will apply just about equally to Debian Linux, NetBSD, or any other variant.
In other words, when you hire someone to work with Unix, that person may have a bias in favor of a particular Linux distribution like Red Hat, or favor a product set like Sun's SPARC based SMP, but the skills will transfer pretty well to whatever you use - and so will the person's loyalties and work focus.