There are many UNIXes. By one definition of UNIX, (minimal POSIX compliance) even MS-Windows is a UNIX.Linux, Solaris, Sun-OS, all of the BSDs, HP-UX, Ultrix, OSF-1, Tru64, EUNICE, Xenix, Hurd, are all UNIXes.
So, for example, suppose somebody finds a problem with named. That problem would afflict all of the UNIXes that run named. You probably would not run named on MS-Windows because MS-Windows has its own name service. So that would be a problem for UNIXes but not for Windows.
Now, you could, if you wanted to, run named on MS-Windows, in which case you have to be aware that a UNIX problem could potentially affect your windows machine.
Most of the problems reported for UNIX/Linux are not actually problems with the OS per se but with applications and services that run on top of it.
I hope this helps. I encourage you to ask questions.
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