[II2II]

The difference between Apple and IBM is the latter lost control of their platform and those who inherited, arguably Intel and Microsoft, had no interest in exerting absolute control. (If they tried, it likely would have backfired anyhow.)

As for Apple, their openness comes and goes. The Apple II was rather open, the early Macintosh was not. Macintosh slowly started opening up with early NuBus machines through early Mac OS X. Since then they seem to be closing things up again. Sometimes it was for legitimate reasons (things had to be tightened up for security). Sometimes it was for "business" reasons (the excessively tight control over third-party applications for iOS and the incredible barriers to repair).

As for the author's claims about their workings being a mystery, there wasn't a huge difference between the Macintosh and other platforms. On the software level: you could examine it at will. At the hardware level, nearly everyone started using custom chips at the same time. The big difference would have been IBM compatibles, where the chipsets were the functional equivalent of custom chips yet were typically better documented simply because multiple hardware and operating system vendors needed to support them. Even then, by 1999, the number of developers who even had access to that documentation was limited. The days of DOS, where every application developer had to roll their own hardware support were long past. Open source developers of that era were making a huge fuss over the access to documentation to support hardware beyond the most trivial level.