Even the IBM PC and XT had BASIC in ROM, which worked much the same way; and it also came with a complete set of schematics and the source code of the BIOS (I don't think the source for ROM BASIC was included, since it was licensed from Microsoft.) While it wasn't truly "open source" in the legal sense and was still copyrighted, it gave users a chance to learn how their machines worked all the way down to the hardware level, and along with that came the feeling that they actually owned the hardware they bought. DOS also came with a version of BASIC and DEBUG, a simple debugger that allowed the creation, editing, and testing of Asm programs. I remember the magazines at the time would have source code listings of simple programs for readers to type in and use. This isn't really "programming" in the sense of "write your own code", but it definitely provided a "catch-point" - some of the more curious might modify the program and see its effects, or do more research about e.g. the instructions and BIOS calls it used, and eventually start writing their own.

Several decades later, you're lucky if you can find even a detailed datasheet or programming manual for the most important chips in a computer. BIOSes are all closed and proprietary, with the exception of minority projects like Coreboot. The relatively few schematics for commercial PCs only exist because someone was nice and neighbourly enough to leak them. I think the gradual shift towards consumer-oriented is part of it, but security also had a chilling effect: belief in "security through obscurity" and the idea that users shouldn't be developers has lead to a situation in which access to development tools and information are seemingly treated as a privilege instead of a right, and systems are correspondingly locked down against users (but they'll all say this was to prevent "malicious attackers"...)

The walled gardens of Apple's iDevices, Microsoft's position on Secure Boot/Trusted Computing, and increasing prevalence of other schemes like DRM designed to take control away from users and strongly push a consumer-oriented mentality are a great evidence of this effect. More subtly, dumbed-down software designed to be "easy to use" take away much of the incentive to learn about how things work that is often responsible for transforming consumers into producers. No doubt the companies like this because they want to be in control and regulate the creation of software; as me and others have said before, "knowledge is power, and they don't want the users to have too much of it." However, I don't think they're ultimately going to benefit from this practice, since by encouraging users in the direction of consumption, they'll be reducing the number of potential good developers in the future.

From that article you linked to:

A kid puts her hand up in my lesson. ‘My computer won’t switch on,’ she says, with the air of desperation that implies she’s tried every conceivable way of making the thing work. I reach forward and switch on the monitor, and the screen flickers to life, displaying the Windows login screen. She can’t use a computer.

Having done some work helping with teaching before - in a computer science course - the number of times I've seen this happen is astounding. A large number of the population seem to have this condition where it appears their brain completely shuts down the moment they're put in front of a monitor, and I think a large part of it has to do with the notion that computers are somehow "magical" and "mysterious" things that don't follow the same rules of the universe as everything else.