Apple's (presumed) controlled leaks tend to be about setting expectations rather than "building hype": they're not going to deliberately spoil the reveals of their own press shows, but they may deliberately shoot down rumors about things their upcoming products don't have. Also, they tend to talk to established venues that don't have a reputation for rumor-mongering. If a "leak" appears on the WSJ, it's often presumed to be a tip from Apple itself; if it appears on 9to5Mac or MacRumors, it almost certainly is not Apple's own doing.
They also try and reveal controversial stuff early so the public can digest it before the event. And I'm sure they have a bunch of people working the social media trying to explain why them taking a feature away isn't such a bad thing leading up to the reveal event (I bet the removal of the headphone jack was deliberately leaked .
