UNIX is basically a simple operating system, but you have to be a genius to understand the simplicity.
An awful lot of successful technology companies ended up being in a slightly different market than they started out in. Microsoft started with programming tools, but came out with an operating system. Oracle started doing contracts for the CIA. AOL started out as an online video gaming network.
Android is very different from the GNU/Linux operating system because it contains very little of GNU. Indeed, just about the only component in common between Android and GNU/Linux is Linux, the kernel.
By the time Apple's Macintosh operating system finally falls into the public domain, there will be no machine that could possibly run it. The term of copyright for software is effectively unlimited.
When Steve Jobs toured Xerox PARC and saw computers running the first operating system that used Windows and a mouse, he assumed he was looking at a new way to work a personal computer. He brought the concept back to Cupertino and created the Mac, then Bill Gates followed suit, and the rest is history.
It became clear to me by 1984 that Microsoft was likely going to be the big winner in the PC software apps and operating system category, partly because of the dynamics of owning and controlling the operating system: that gave you enormous power, and I came to see Bill Gates was fierce competitor.
The definition of an 'operating system' is bound to evolve with customer demands and technological possibilities.
Nokia and Research in Motion needed a modern operating system. They could have bought Palm or Android before Google did, but they didn't. Today, it's probably too late, and at the time they would have been criticized for overpaying, but as they say - shift happens.
In television you go in with this operating system that it is a crapshoot.
There is no neat distinction between operating system software and the software that runs on top of it.