I think that's a bit doom and gloom. We now have github, it's easier than ever before to copy code and release it as your own.
As for BSD a search of my (partial) ports tree finds 19326 Makefiles of which 102 contain the string github. Thats 0.5 percent, which tends to argue against your claim.
That's just the easiest measure I have at hand. Would be interested in others and their findings.
I don't mean my mom, but I do mean to imply (without evidence) ordinary non-Norvig coders who aren't steeped in Unix lore.
Does ports really do what Github does, or does it do what apt/rpm/yum/pacman/etc do?
The ports tree is for handling distribution of compilable/installable software for the platform, and you synch it from a server, then build. It's not really intended to promote the branching and modification, and social aspects that github does.