Absolutely. Most 12 year old kids don't know about file size units. Relative file sizes, converting between units etc. There's so much incidental learning that occurs too. The other day i was discussing file sizes with a student and we observed that there was a difference between a file's reported size vs size on disk. This led to a great little segue about physical disk structure, tracks, sectors and clusters. The boy was fascinated with some lower level detail. All that learning would have been lost if we were using a gimped cloud based FS.

These days, those are abstractions as well. That's basically the API that the mass storage controller presents to the OS. I'm not sure you could explain a hard drive to a lay person anymore. Most of the time, I'm kind of surprised that they work at all.

Only if you are using them wrong; while I think iPads are poor tools forany purposes, including that one, from a UI perspective (or, at least, inefficient by the time you address the interface issues), iPads and Chromebooks don't restrict the ability to teach full-spectrum computing, as, they are perfectly capable tools for accessing and interacting with general purpose computers.

Now, clearly, the exact details of how you use them in that teaching and th supporting infrastructure might be slightly different than if you were giving students PCs, but then, you need a network environment with educational infrastructure if you are teaching full-spectrum computing with modern relevance anyway, and the detail are going to vary by what you use on the front end. That doesn't rule out any front end choice, it just means that the front end choice impacts other choices.