My experience of corporate IT is that "X is better than Y" is a long way down their list of priorities.

An IT department in a large organisation will typically customise the OS heavily, meaning that upgrading the OS (such as from XP to Vista or Win7) happens rarely, and switching platforms is unheard of (I've seen this once, when switching from Unix workstations to cheap NT4 boxes).

What I think is more likely is the use of Linux or OS X machines to remotely connect to Windows desktops or Windows virtual servers.