I honestly don't get why there are still a bunch of non-Linux/BSD servers, at least if the goal is to do UNIX-y stuff.
I haven't touched AIX or HPUX in probably a decade and I thought they were a weird idea back then: proprietary UNIX? Is it still 1993?
At the time (10 years ago) I worked for a company with enormous customers who had all kinds of different deployment targets. I bet that list is a lot shorter today.
I hope so, for their sake. shudder