They are paying for support, not the software itself. A long time ago you could go to the store and buy a box containing the CDs for Mandrake Linux as an example just like you can do with windows right now. You were not paying for the software itself but for the media and the box. Even when you pay for a binary on windows, you pay for the service of them compiling it and making it available to you, not the software itself since it is free/libre.