If that were the only point to an operating system, why doesn't Windows have a monopoly in all areas of computing?

Surely there are other considerations beyond stability to be had when choosing an operating system?

Free beer being one of them, and people are willing to put up with lots of issues, even if it is given free warm.

A windows-system is always warm, even if it has nothing todo...and it's not even free ;)

Windows pays for the fridge.

I don't think people are using PF to write software on top of -- they use OpenBSD specifically to run PF. You should look at upgrading OpenBSD in this use case to upgrading the firewall software.

It's a different case than mere "I compiled this application 6 months ago and I want to run it today", which is the "stable API" part of an OS that you mention.

Since the BSD's are not meant to run proprietary binary's on top, just recompile your code and everything is fine.

Linus want's that the OracleDB's of the World can run on his system...that's is fine i think ;)

NetBSD makes a point of preserving backwards binary compatibility.

Correction:

FreeBSD is also compatible down to FreeBSD 4 (March 2000)