Personally, an article like this, with its main diagram and high level descriptions, would have been enormously useful back when I was just starting to learn the dark arts of computer programming.
If your Point of Sale systems are running some embedded form of Linux, and all HW access is abstracted away from you, then you're probably right.
On the other hand, if you are writing code that deals with external HW signals, performant memory access, ISRs, an RTOS and their many features, etc, then this article serves as a good basic foundation for the "software" side of things. Ie what actually happens when you hit the "build" button in your IDE.
From, a long time embedded software engineer