mutant:
Large servers are the only area where Linux is more cost effective. The reason is simple. Linux is cheaper to run because many of the programs including the OS are free. However, you need a knowledgable and skilled person to administer them. This works fine in a server room environment where one engineer can maintain many machines.
However, in the desktop (and small business server) environment this becomes a serious problem because the user does not have the expertise the configure the system themselves and often there will not be a specialist engineer, just the boss or a technically minded employee doing it as a bolton responsibility to their normal job.