While I agree with the idea of making use of what Linux provides, especially in low-level software, what you said in this particular comment is wrong in an incredible number of ways.
For one thing, your historical interpretation dismisses the fact that Unix was expressly written in a portable language, which was revolutionary at the time, and without that would never have gone beyond DEC minicomputers. It also dismisses the benefits that occurred specifically because of forks/reimplementations such as BSD and Linux. You seem to think that Linux is the pinnacle of Unix evolution, and beyond it is nothing but better Linux, which seems rather short-sighted to me.
Alternative implementations of parts of a system improve the longevity of the system, since different implementations may end up adapting better to new circumstances down the road.
Portability has mattered to the free software ecosystem since day one. Just like no one company has all the best programmers, no one operating system has all the best programmers either. We can gain from people on the BSD platforms, and they can gain from us. Remember that much Free Software started on Solaris or other non-Linux platforms, and even now MacBooks are becoming increasingly popular as programming platforms, and there's no reason to shun those people. The Free Software Foundation releases software portable to Windows (with great derision from the OpenBSD folks), treating that software as a gateway drug to help lead users away from Windows.
Yes, we should take advantage of advancements in Linux, and push for more, but we also shouldn't completely throw away portability.