The author doesn’t actually say which of the possible upgrades he personally did, and how he benefited from it, and thus how he has suffered since the ability to custom upgrade components was taken away. I think he just likes the idea. He won’t like the reality of the hassle of a PC, and I hope he writes a follow-up article when he “returns” to Apple. And loads of people I know who have moved _from_ a PC to a Mac actually have benefited, without the need to then upgrade the already-powerful (Apple) computer they now own.
Anyway, the need to upgrade was driven by software that was ahead of the curve. This was good, people were making and improving Mac software! And they still are, without the correspending need to upgrade RAM to make it run. It just runs. I started with a PowerBook 170 (maybe it was 190?), and worked my way up through models, upgrading ram or HD as needed. I worked with people using windows... holy moly, their misery was non-stop. And it’s still that way!