"Free" doesn't mean "free"

The cost of an operating system is just a drop in the bucket compared to all the additional costs involved with computing.  Just ask ABB....

IBM lands $1.1 billion IT services deal
IBM Global Services will take responsibility for the operation and support of ABB's information systems infrastructure in 14 countries in Europe and North America, representing some 90 percent of ABB's information systems infrastructure.

Yep.  That's with a “B“.