There are two solutions to this problem:
1) Leakers stop leaking shit just so they can get their 15 minutes of internet fame
2) The entire industry moves to a model where they announce games ASAP after 'conception,' (so as soon as any form of concrete plans are drawn up, maybe even before) something that very few industries out there actually do (not even movies). This would, due to the volatile nature of game development, lead to many more damaging stories about delays, cancellations, etc, most of which will probably still come from leaks anyway; it will also lead to more damaging reports about games taking "way too long!" as even 3 years is a long time in the gaming industry. Meanwhile, on the worker's side, carefully-constructed marketing schedules (which are created by people; marketers and business strategists aren't evil robots, after all), stock jumps from well-timed announcements, and the very notion that developers can surprise people with an announcement are all thrown out the window.