Also, the hardware. (It is much harder to make it work reasonably well across so many platforms without an army of full time devs.)
That's a genuine question, I just read yours in a few different ways.
However, I'd argue that relatively small details just fall into the category of overall interface polish. Not just aesthetic people polish, but the category of things that make you put your hands to your face and scream in frustration.
But yes, there are definitely important details in other layers that are worth considering. I think that when people make comparison's though, beetween macOS' level of finesse and something else, that finesse is defined by polish at most levels of interface with that hardware and so on.