Apple iOS 9 brings a major shift to company's policy and will now allow developers to create extensions that block web-content on their devices. There was no public announcement regrading the new feature but developers running iOS 9 have found the "content-blocking" feature enabled in their device's Safari browser settings as shown below.

New Content Blocker App Extensions for Safari (on iOS 9 and OS X El Capitan) allows targeting of subsets of web-content (display ads, images, navigation elements, popups, scripts, fonts, style sheets, media files, cookies etc.) blocking them from being shown or loaded.