Job security is basicly Cringely's position. Macs are easier to maintain which would mean less IT staff which would mean losing jobs. So IT is artificially backing Windows to create work for themselves.
I know a lot of folks that do Windows support. Most of them would LOVE to ditch Windows in favor of Macs or Unixen, even if it meant their job. What keeps Windows in the business place? Same thing that keeps it in the schools, famliarity. People use Windows at home so they want Windows at work. They want to be able to move from business to work without having to really learn how to use a computer. Just walk through the same rote commands each time. They want to use the same software at home as at work. Comfort. It sucks, because they're getting comfortable with a horrid system, but its a much better explaination than a vast IT conspiracy.
Then there's software compatibility. You've got Office on the Mac, ok, but what about all the other crap out there that's Windows only. If there's one important piece of software that your business needs which doesn't run on the Mac, you're screwed. Virtual PC can help, but now that's an extra expense and complication. It sucks, but its at least reality.
Then there's vendor lock-in. Companies have been using Windows. They're trained in Windows. They can get Windows monkeys cheap. All their systems interconnect using Windows-specific protocols. This is the natural result of having a single company-wide platform, people forget about compatibility. When you try to introduce something new into this system it doesn't fit well. A typicaly compuxenophobic (a word I just made up meaning "fear of computers that are not like your own") company will blame the new computer rather than step back and look at the box they've painted themselves into. So the new Mac looks bad because it can't talk to the broken Exchange server. It sucks, but its reality.
Then there's $money$. When you've sunk $NNNN thousands into Windows, you're reluctant to throw away that investment and switch to something better even though its good economics. They call it "throwing good money after bad" and its something people do all the time. Human nature overriding business sense.
Then there's the Apple price myth. Mac hardware used to be extremely expensive. In the last year Apple prices have plummetted. You can get an iBook for about the same as a comprably spec'd out Dell laptop. Most people I talk to don't realize this. When I tell them I got my iBook for $1600 they're amazed. Why is this? Because Apple isn't advertising it. One of the single biggest selling points for a PC is price. "I know its crap, but its cheap" is the usual explaination given by a PC user. For the first time in 20 years Apple can match PCs on price! They should be plastering this on billboards across the country. Here's Apple's new can't miss ad campaign: "Brand new iBook! $999! Holy SHIT!" "1U XServe! $2799! I think I just wet myself!" Instead they put up touchy feely ads with people waving their hands and telling us how much they like their Macs. This soft sell is pathetic. Apple can win on numbers and they should do it.
And then there's the myth of MacOS. OS X is still seen by the general public as a toy. Windows users don't really understand what a whole new world of stability Unix is. Apple should be writing up ads like: "Microsoft recommends you reboot your NT server every week. Apple recommends you take your weekends off." "At Apple, its not corporate policy that your computer will crash." They dance around this subject with their "it just works" ads, but they should switch to a hard sell. They've got the superior product, sell it on numbers and facts. Soft-sell is for when you have nothing to sell.
PS I'm writing this in an iBook.