[SauronOfMordor]

Apple can control the apps, but they cannot control the browsers.

The browser is just another app. They can update the browser to not access unapproved URLs.

[dfwgator]

They can simply block all traffic from a certain IP address.

[monkeyshine]

But there are lots of browsers to choose from. I suppose they can also deny browsers but they may run into anti-trust issues.

[rxsid]

"Apple can control the apps, but they cannot control the browsers."

The browser is just another app. They can update the browser to not access unapproved URLs.

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And...if need be, the tel-coms that control the internet backbone can filter or stop traffic altogether.