I'm a little on the fence here.
One one had, developers taking great care to make an announcement big, worthwhile, and exciting, only for it to be leaked, can seriously deflate those working on it. That's kinda shitty, and I can totally understand where Cory's coming from. People don't like their hard work, especially something like this which is time-gated to a specific event, to be unearthed before it's supposed to.
On the other hand, from a consumer point of view, I don't see how anyone perceives announcement leaks as "spoilers." It's an announcement, not a description of things like major narrative happenings in the game. You simply know that something exists before you were expected to know it exists. If Mother 3 ever gets announced and I suddenly find out about it a week before the announcement, it doesn't really change much for me - I know the announcement is coming, and there's a potential to learn more about the game through the official announcement. At the end of that week, I know just as much as anyone else does. It's not like being spoiled on, say, Citizen Kane rosebud was his 401(k), where I would be annoyed that possibly everything before that revelation in the film is completely devoid of mystery, but with announcements, you're basically being "spoiled" on something that you don't even know could exist.
Surprises are nice, and the excitement of hearing about something new at E3 or a Direct or what-have-you is pretty cool, at least being able to experience it in the moment and even discuss it with others. But for me I don't feel like I've "lost" anything by hearing about it early. If anything it makes me excited to see the official announcement, cause if it's something I've wanted I can get hyped for it a little early.
But regardless, in my view ideally leaks don't happen. It's nice information to gain, but it's nothing earth-shattering. God forbid I have to wonder for that extra week hate-posting "Man I really hope they make a sequel to Fisherman's Bait: A Bass Challenge or else I'll...I'll...I'll continue to keep wanting it."