On iOS, Apple’s more conservative approach to blocking ad tracking may relate to the fact that a large number of apps rely upon ad networks for monetization, and that Apple itself has a horse in the race with its own iAd program.
Apple adds new “Limit Ad Tracking” feature to iOS 6
http://appleinsider.com/articles/12/09/13/apple_adds_new_limit_ad_tracking_feature_to_ios_6
