The main disadvantage of most computing devices is that they offer too many options; making them mentally unwieldy. A "single purpose device" is created to support just one purpose. The Kindle is perhaps the most famous example; it practically created an industry. Sure, it can do more than just present books, but everything is designed to support reading.
Ideally, there would be a "computer", where every aspect of it was designed to teach computer programming.
I often fantasize about a device designed solely for producing new writing. It would have a nice screen, and a nice keyboard, but only a very very limited web-browser, and would sync with Google Docs, Office, or something similar, so that you can do the more advanced stuff elsewhere.
Such devices are about empowering the user to go down a specific path; one they choose as soon as they start interacting with the device.
Kindle -> Reading
Typewriter -> Writing
Hammer -> Hitting things
"Power to Basic" -> Learning to program