Not sure if trolling or serious.
Knowing how to drive a *nix operating system is part of any well rounded set of tech skills. One reason to get started with Linux is that you can learn it for free instead of having to pay for Microsoft training or the licenses to set up a lab in your own place.
If you're doing security on the red team, either the tools are linux based, or you've got to work to get the Linux tools working in a Windows environment or run Linux in a VM.
Now I wouldn't call what I do traditional, nor would I say that I work in the "IT Shop" for my organization per se. I use skills developed over time in the following OSs for the following purposes:
Backtrack/Kali Linux - Red cell work, forensic acquisitions of *nix like OS's including OS X.
SIFT 2.x - Linux based forensics on all operating systems
Windows 7 - Windows based forensic analysis and email
OS X - Used for multimedia preservation, software development and as my host OS for virtualized systems.
As for your statement about Linux on the server dying, I think this chart goes against what you're saying.
