I worked as a contractor on an IBM project a year or two ago. I have to say that my experience backs your post up. All of the desktops were Windows based. The servers were Linux, but that was mandated by the customer.
Even worse, we were not allowed to use open source components unless they had been approved by IBM's legal department. We got into the ridiculous situation that we had to change our code coverage tool from one that was based on the GPL to one that wasn't even though the instrumented code it produced was never shipped to the customer.