You need to take remedial set theory. There are how many closed-source OSes out there? For all you know I could be a fan of BeOS, OS/2, or (*gasp*) Windows.
Actually, I don't love closed-source so much as I have been quite forcefully disillusioned from buying into the FSF propaganda that open-source is magic pixie dust that makes everything better unilaterally and has no disadvantages whatsoever. Comes from multiple attempts over a solid seven years and change to try and get a really usable, pleasant user experience out of any of the eleventy billion mutually-incompatible Linux distros.
I do like Haiku as it's shaping up, but then Haiku takes the unorthodox but eminently sensible approach of allowing open access to the source but forbidding forking, so you actually get a single cohesive user experience.
What makes you think the Haiku licence forbids forking? It's MIT licenced which is even more permissive than the GPL. You can literally do whatever the hell you want with it, including refusing to release the source to your own changes.
We've been here before John, your problem with the *nixes is that you don't know how to use UNIX to do what you want to do, nothing to do with the licencing model of the code*. Different strokes for different folks.....
There's a big difference between Free Software as defined by the FSF and Open Source as defined by the OSI too.
*Correct me if I'm wrong but you'd be just as baffled by the closed and proprietary HP/UX and AIX as you are by GNU or OpenBSD.