I reckon this is actually a fallacy. Sure, you can pick up a Windows tech on any street corner, and you can probably find them with an MCSE to boot. But do they have any actual experience? Are they going to know about good security paradigms such as privilege separation and good firewalling? What about getting software and computers on a network talking to eachother? Do they have any experience with your other business software? I'd say chances of a lot of those things being true of most of your 'street corner techs' is pretty low. I reckon "I can pick up a windows tech on any street corner" probably means "My brother's oldest knows a bit about Windows, and e sounded really enthusiastic when I offered em the job..." more often than is good for the industry.
In my experience, good Windows techs cost just as much as good Unix
techs. But often Windows techs, like their software, come bundled with
a lot of established opinions and special deals on what software you
should buy - i.e. Microsoft. Often they don't evaluate software well
because they're (perhaps unconsciously) siding toward what they know.
This is not a problem in most cases, except with Microsoft we know that the software costs a lot more than equivalent FOS Software; so by getting a Windows-only tech you're more likely to be spending more money on Microsoft software in the future. While I see one of the faults that the FOSS mindset brings is 'Freedom or death' bigotry - i.e. they would refuse to use for-money software (e.g. SAP) even where no real equivalent free software exists - I think most of us are pragmatists and heterogeneous free and non-free software environments are the business reality that most of us would accept.
Funnily enough, I hear today that the Commonwealth Government is hiring senior IT techs from the UK because they can't get them here. So the 'one on every street corner' idea doesn't really hold much water.