To be fair, Wii U only leaked because of 3DS' ESRB leak. The roster probably would have stayed hidden if it weren't for that.
Brawl wasn't really affected either due to no one believing the leakers, similar to how Verge's early leaks for this game were harmless because not many believed him.
Plus, both Sakurai (and I think even Bill, right?) have gone on regard to state they're aiming to avoid major leaks from happening again. Also, it's mainly about the timing: Nintendo 9 times out of ten does their final game focused info dumps a month or so before release. I can't really think of any recent game that breaks that trend, as even outside of Directs, they do final press releases in that same timeframe as well. That just seems to be how their marketing works (IMO, at least). I honestly think the last bit of news is coming soon, so I wouldn't worry about it.