There are plenty of practical reasons to think that the iPad (or a device like it) will be a large success. I completely agree that there is a target market that wants a slick looking device that just works, and Apple is positioning itself to go after that market. Most of those people don't care in the slightest if they have to go to Apple to get a battery replaced, they'd probably want to buy a new device at that point anyways.

I think the concern here is the precedent that Apple's success in this market would mean. Apple is notoriously hostile towards their development community, and is providing increasingly locked down platforms which make them the gate keepers for certain types of innovation (want integrated voice recognition on the iPad - wait for Apple to do it). If Apple succeeds here, others will feel they can create the same sort of locked platforms. You can already see this happening.

There's also a concern] for the future developers. If their homework requires a word processor and a web browser, then their parents might never see the need to buy them a general purpose computer.

True, especially because an iPad will not replace the PC/Mac under the desk: Where do you let your children (or for this example teenagers) play gamey like CSS, Gothic 3 and so forth? Certainly not on the iPad. It is the same story with video encoding, rendering or even burning a cd/dvd. The """young hackers""" will still have their platforms to play with. Even if somebody only had an iPad, he might become a web security geek.

Exactly. And we have systems like lego mindstorm that are designed to get people interested in hacking. The universe of possibilities is expanding, not contracting.

And nothing, not a single obsolete machine, ever truly disappears. I'm confident that COBOL will still be running somewhere 2250.