Walled garden is a general trend whether on the web or on devices such as the iPad and game consoles.
Such control have advantages, but it facilitates abuses. It even requires some of them: if Apple allowed interpreters to run 3rd party code, it could introduce a loophole that may create the equivalent competing store. Massive online sandbox games face a similar problem with the ability to build arbitrary stuff: they generally don't want their player to build or draw… inappropriate depictions.
All this is not really a problem as long as it stays confined to a specific purpose (such as playing games), or a specific community (such as here). Inevitably, curation means control, enforcement, and lock down. We need that.
What scares me is the gradual disappearance of free, uncontrolled space. Both online and on devices. Walled gardens used to be confined to game consoles. Now they start creeping up on general purpose computers. The iPhone and iPad where a significant step up. And now even the desktop isn't safe. The iStuff made it acceptable to lock everything down in the name of the safety and convenience.
We are losing the war on general computation.
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Besides, there is a link between the freedom of the network, and the freedom of the devices. Without free software, you can't have a free internet: people will just used the (proprietary) software that's available to them, and that software will naturally steer them to "safe", controlled online spaces. You quickly get a cyberpunk dystopia where you have to break the law, perhaps even risk your physical safety, to run programs not approved by some corporation on your device (if they're still officially yours by then, and not "leased" forever or until you look at them funny).
And of course, without a free internet, you'll have a hard time organizing and implementing free software —especially if the software is susceptible to free the network free again —it will be shut down as "unlawfully facilitating circumvention" or something.
The simultaneity of the gradual locking down of both devices and network is no coincidence.