Windows 3, 95, NT, and 2K each saw significant changes in where and how major system functionality was presented.

During the same period I was using numerous Unix and Linux platforms (and still do). Those have largely seen far less substantive change at the shell and system level, with a few notable exceptions.

I'm not discussing Linux GUIs, which have been all over the goddamned map. I've used twm, fvwm, fvwm2, VUE, CDE, WindowMaker (my preferred option), GNOME and KDE through multiple generations, Enlightenment, various of the 'boxes (black, open, flux, ...), ion, xfce4, ... And those are the ones I've trialed to some significant extent. I've at least fired up and looked at virtually all the options mentioned on the XWinMan page: http://www.xwinman.org/

There are several fairly central components which have changed fairly markedly. The shift from telnet to ssh, multiple iterations of firewalling, various scripting languages of preference (bash, perl, python, an oddment of others), mailers (sendmail, qmail, anything reasonably sane, mostly exim and/or postfix now), and of course, the whole init replacement clusterfuck.

But the notional concepts of files, filesystem, shell, utilities, pipes, etc., has remained consistent, and even across several utility / server replacements (particularly ssh and mailers), command-level compatibility has been preserved to a remarkable extent with previous options (e.g., rsh and sendmail syntax).

If Microsoft can only be relied on for five-year stints of "having learnt this lesson" then they have not learnt this lesson.