WHOA WHOA WHOA. POKEMON X AND Y, ARE YOU SERIOUS?
If you know anything about Pokemon, you know that Pokemon leaks happen so often, I'd call them goddamn inevitable--almost tradition. CoroCoro scans, early release dates abroad, mistakes in trailers, hackers... you name it buddy. Remember that GameFreak is not technically Nintendo. It is a separate entity almost, but only owned by Nintendo.
I like to think of Gamefreak like a Clownfish, acting on its own, while Nintendo, the anemone, provides it a home. BIG DIFFERENCE.
And the brawl leaks happened very far into development, near release dates. That's the difference with the Palutena leak and the real leaks during Brawl-era.
EDIT:
Nintendo, as the giant that it is, has much less room to make mistakes. GameFreak, on the otherhand, is not so stable (information-wise) and history shows that to be true.