In college I had a class called Unix Operating System were we used a book called "Guide to Unix Using Linux". I thought it was odd that the class put so much focus on Unix while we were actually using Linux... why not just put that focus on Linux instead? In the "real world" after college, I only touched Unix once, as Solaris running Oracle 11g. Everything else I use is Linux. In the real corporate world, from my experience as a consultant being involved in many different and diverse environments, Unix is rare and only used when necessary. Linux is everywhere, and always used unless something else is required.
No one takes a "How to use Unix" class to learn how to use OSX and Android. In fact, I've never seen a production database cluster running on a Nexus 5 at any of my clients.
