Yeah the cases are what interest me here. It comes down to a matter of opinion by judges, and that opinion can be really fine hair splitting. Like, is it 'expressive' to lay out your buttons in a certain way in your UI for your paint program, but not expressive to choose the layout of microchips on your video card? I imagine there must have been a small handful of pivotal cases that decided that issue, and put software into the domain of copyright.
If it wasn't for this quirk of history, there wouldn't be copyrights on our software.
And it all pivots on what some Judge, likely a technologically ignorant one if today's standards are any indication, decided in some case way back when.