Consider this:
80% of all hosting companies use Linux, WHY?
Microsoft used to use Linux for the MSN product. (I know this first hand as I worked as an L3 for the MSN project back in the day.)
Well lets start with the cost of ownership/operation.
Linux when configured correctly requires less hardware.(With Linux you don't need to run Windows or should we say xWindows. Get it x-Windows. Plus you can remove anything you dont use.
Linux is more secure. (If you know how to secure it correctly. --- RTFMP)
Linux is open source so the cost of OS ownership is free. (If you know how to download and burn an ISO.)
Linux is more stable. Hummm when was the last time you had to reboot your Windows machine?
Well I could go on for years. Suffice it to say I run a small hosting company and I use all Linux.