To save websites from ads, they're destroying the websites
It's not iOS alone, of course: Apple has included this ad-blocking capability in OS X El Capitan's Safari 9 browser. That'll hurt Google for sure, given that Safari is the dominant browser in the Mac world, which is the only growing PC segment today.
If Microsoft feels the need to do the same in Windows (after all, it has no ad business to threaten, nor does it like Google much), Google will end up able to serve ads only to Android devices, Chromebooks, and Chrome-using computers. Chrome is the most popular browser today, but that could change if it ends up being recast as the "advertising browser."
To use another war analogy, ad blockers have to destroy the village to save it. That made no sense in the Vietnam War, and it makes no sense in the content world today. But it's the war we're collectively waging against each other.
Apple has pushed it to the level of mutually assured destruction. You know that advertisers, Google, and the social networks are readying their own technology missiles. They have no choice.
Even worse, Apple is making itself the gatekeeper of mobile content
Apple probably doesn't care about publishers; it's long looked at that industry as an annoyance that at best relays its marketing messages at little cost.
Its new News app in iOS 9 has no clear business model for the publishers who supply its content — other than iAd-served ads, of course. It's a poorly designed app that makes it too hard to find the content you want; established apps like Flipboard are much better.
But Apple plays the long game, and News doesn't have to be good. All it has to do is be the only option that users turn to when all those other websites are devastated by the holes blown in them by the ad blockers. If other content apps survive and use an iAd competitor, Apple still controls which ones are available and can take a cut of any in-app purchases such as subscriptions. Thus, Apple will control much of the safe distribution and revenue stream for mobile websites. Yikes!
Duck and cover. And hope they all pull back from the brink.
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