And pretty much all major programming languages and libraries are given away for free too. Someone tries to introduce BitKeeper, a commercial version control system, for the Linux kernel? They won't stand for it, some's gotta clone it and give the clone away for free.
Hell, I've heard loads of people here on HN complaining when a SaaS company introduces features exclusively useful to large corporations - like single-sign-on integration - then wants to get paid for them.
There's a handful of exceptions. For example game developers will pay $$$ for "Unity" and store their assets in "Perforce" and suchlike. And I believe it's possible to pay for Visual Studio.