The true Unixes, like BSD or Solaris lag a long way behind
Mac, I would suggest that the reason is that most of the "true Unixes" like HP-UX, Solaris, AIX, Tru-64 are expensive, proprietary and intended to run on proprietary hardware (HP, Sun, IBM and Dec / Compaq Alpha respectively), for which proprietary drivers exist. Much more like the original Apple Mac SW / HW model.
You are right, though, that even FreeBSD and OpenSolaris (rather a johnny-come-lately to the open-source world) haven't been embraced like Linux. Why is that, do you think?
SD