They need to find a balance between secrecy/surprise and fan base communication.
I understand that it's very cool if there's unlocks led no one saw coming when people play the game, or if they get to reveal characters when no one was expecting them to, but here's the thing with those: The surprise of something like that is short-lived. If there are secret unlockables they will be posted to forums the instant someone gets them. With reveals, it doesn't at all ruin the surprise to say "yes we will be revealing more characters at this convention". If anything that builds more hype.
On the reverse as well, it would have been fairly simple for them I say to all the people asking about TGS " We don't have any character reveals planned but watch out for some cool new stage demonstrations!"
Basically what I'm trying to say is that they would benefit a lit more from telling us a little bit of negative information than flat out telling a nothing.
All that being said, I'm not mad or anything really, but it was still a bit disappointing to find nothing new today.
I really think they should say something like "There will not be any more characters revealed, but there will be some secret ones in store once the game releases." Or "We've got a couple more character announcements coming up in the next month so stay tuned". That really wouldn't ruin the "surprise" for me, and would only help their game's hype.
tl;dr: SuperBot needs to give their fan base SOMETHING to go off of, because a tiny bit more surprise is not worth disappointing this many fans.
All that being said, I'm extremely pumped for this game and have seen a great product thus far. I look forward to whatever else we end up finding out!
I don't think I'll be around the forums for the time I'm playing the game unlocking everything.
I'm doing the same thing right now with Serebii for Pokemon Black 2, I would rather be surprised.