Robert X. Cringely in May the Source Be With You thinks that Macs aren't getting in large organizations because they threaten the livelihood of IT staffs:
If you recommend purchasing a computer that requires only half the support of the machine it is replacing, aren't you putting your job in danger? Exactly.
Ideally, the IT department ought to recommend the best computer for the job, but more often than not, they recommend the best computer for the IT department's job.
He is also digging around why they prefer Linux over Mac OS:
Again, it comes down to the IT Department Full Employment Act. Adopting Linux allows organizations to increase their IT efficiency without requiring the IT department to increase ITS efficiency. It takes just as many nerds to support 100 Linux boxes as 100 Windows boxes, yet Linux boxes are cheaper and can support more users. The organization is better off while the IT department is unscathed and unchallenged. [...]
Macs reduce IT head count while Linux probably increases IT head count, simple as that.
I'm among those who claim that Macs have a lower TCO than Windows-PCs, and for many more tasks than the creative ones people usually think Macs are made for. A couple years ago, my better half was doing IT support for a Mac OS-based operation of 200 people spread in 20 cities, alone! Would you imagine one person supporting 200 Windows-PCs, even on the same building? Me neither.
I think that one of the main reasons why Macs aren't getting into corporate IT is simply ignorance. It is amazing to see how many IT people, and in particular CIOs, are simply labeling the Apple world as unknown and uninteresting. Ignorance leads to fear for most people, and those guys -- who you would expect to stay informed of everything that is new and innovative in their industry, which come from Apple more often than not -- tend to limit their curiosity to what is the latest Windows vulnerability of the week.
The rest of the article is focused on IT outsourcing, in particular the current trend of Indian off-shore operations. Only time will tell us how this trend will evolve, but I don't think it's going away anytime soon.