Mac OS X is a high end niche product that many people have decided to pay for and purchase.

The problem with Open Source is lack of clear goals, as you will discover when you try to install TV cards fro your Linux box. Gnome 3 is another example. A lot of effort is invested in matters that really do not improve userbility but which are meant to give more freedom.

At some point, people find that they would rather do away with the freedom for efficiency. The same a toll road - fewer exits and entries (freedom) , costly (tolls) for efficiency.

And some aspects of this free linux have been funded by the same DOD and other non-free companies. Most of the time, Open Source is used as a cost cutting measure to crowd source a solution, or to make it widely adopted for other benefits eg Android to sell Google Services