Can't speak for the parent, but I have similar thoughts with my kids. My reasoning is pretty simple: technology that's already finely packaged and integrated might as well be magic, and it really makes it hard to want to open the hood and tinker with stuff. Personally, I think tinkering with computers had a big impact on me because it revealed that computers are just another kind of machine, subject to tweaking and understanding. I don't think of them as inscrutable monoliths as a result. I'd like my kids to have that same attitude toward technology in general, so the more they can build for themselves, the better.

Regarding why it might be the only hardware, I'm probably not as extreme on that front, but I think I can understand the motivation. With a choice between the slick user experience of a well-integrated touch device or the hacked together experience of roll-your-own Linux on roll-your-own hardware, I'm not sure how many kids would voluntarily choose the harder (but ultimately more rewarding) road. A certain amount of struggle and adversity seems to be important for making knowledge seem worthwhile and for pushing kids to explore. My own kids are most proud of themselves when they do something that's not easy for them, even though they usually complain the whole time they're doing it.

When I was in grade school, I started reading library books, and gravitated towards the programming books. They were mostly BASIC on Apple IIe hardware. I used BASIC on whatever hardware I could get my hands on, and my mom bought me a calculator that had a BASIC interpreter. Even once we got a PC, its capabilities were sub-par. I didn't get a machine that reflected the state of the art until I built one myself in the late nineties.

Having severely-limited hardware made me invest lots and lots of time into figuring out how it worked. I would like to pass that experience on to my kids, so they can be masters of their own technology world instead of passive consumers of other peoples'.

Did you screw up your machine? Do you know how to re-install the OS? Here's a printout of the page that tells you how. Have data you didn't back up? Well, here's a protip, you can mount the hard disk on another machine, maybe your sister will let you use hers.

I don't want to speak for vinceguidry but when I was a teen my first car was a Mazda RX-4 with a blown tip seal. My job (with Dad's guidance) was to swap the blown motor for a fresh one and if I could get the car running it would be mine. I remember fondly both the car and the time I spent wrenching on it with my Dad.