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I don't view the iPhone and iPad as "computers" or "personal computers" any more than I view my cable TV set-top box or Sonos speaker that way. Both are very powerful devices with Linux operating systems. But I don't expect to be able to program them. The iPhone is an appliance that can download "apps" that Apple permits. When I want a "computer" I open up my MacBook.
How does letting people freely sideload apps conflict with this philosophy? You can still use your iPad as the world's most expensive e-reader if you want, letting other people run Linux on it doesn't somehow ruin your experience.
Everyone likes to say “but would Apple would lose the $100/yr from all those hobbyists.” How many hobbyists do you think are out there right now paying $100/year just to load some apps on their phone? Can’t be more than 1000. Even if it were 10,000 that would represent $1 million/yr in lost revenue for Apple. That’s less than a rounding error on just one quarterly report. They really don’t care about that!