Y'all act like E3 is going to reveal every single character in the game. We'll probably see a newcomer or two, but the whole roster is still uncertain until release, and all the unlockables have been found in-game.
You act like a boatload of information is an unreasonable expectation.
Point 1: The 3DS game has a summer release date, so at the latest August
Point 2: Sakurai has expressed distaste about video content getting spoiled on youtube
Point 3: Sakurai mentions each newcomer getting a video celebrating their inclusion
Point 4: Unlike before, E3 won't have just a 5 minute video of Smash. It will have: the actual digital event that may include smash content + an invitational tournament + a 90-minute Q&A session with Sakurai.
Given all of these there is nothing illogical in assuming that we'll get A LOT of information on the game, and since at most they'll have only two more months before releasing the first game, they'll want to show off some of those newcomer vids with as much time as possible. Even if not that, the direct alone had five characters, four vets and one newcomer. So it's not unreasonable to imagine at least five character confirmations.
I also imagine that given Sakurai's emotions on spoilers expressed long ago that they'll prefer to show off the newcomer videos at their pace instead of waiting on Japan/reviewers to get their hands on the game and then promptly reveal the whole roster to the world in a puff of anti-hype. So given this it wouldn't be surprising if they pull a Mario Kart and reveal all the characters before release and still have you unlock some of them when playing the actual game.