Good comment. Additionally, it *COULD*, MIGHT, be an attempt by a CIO/CTO/whatever to get rid of non-approved software they feel might be a security risk. With the increase in penetrations of private networks on the rise (or at least being highlighted more in the press), it would make sense.
While I agree with the sentiment that MS may not be the best choice, I can sympathize with the goal. Also, if members of the IT staff are criticizing or trashing technology decisions, that will only make life harder (and sometimes unnecessarily so) for management. Users bitch about IT anyway, so I can see wanting to get ahead of that.
Finally, I know a few folks who worked in IT at hospitals, their budgets were nil. There may not be $$$ available to support different OSs for various functions. Just another perspective. I don't think such a draconian approach is a good one, I can understand the sentiment.
Hypocrisy Disclaimer: My current employer is Windows-ONLY on their network, but I have my Mac working just fine, so I'm glad they've looked the other way - thus far... [shrug] I suppose it's easier to "see their perspective" if I don't have to live with it.