It's OK, stuff like that happens sometimes.
Anyway...
I see where you're coming from here, but... You don't think they might start working on the character(s) early? I mean, yes, the ballot hasn't officially ended yet, so it might seem unfair, but they can probably check the current results and see if any characters have a strong lead. And let's not forget that popularity isn't everything. It does play a big role, but the characters also need to actually work as fighters. Let's say Sakurai promises us this one character from the ballot, but then some technical issues come up during the development of that character. Or perhaps Sakurai can't figure out the right moves that would work for the character. Something like that. Well, if something happens and Sakurai simply can't put that character into Smash, the fans will likely be really upset by this, and will probably feel lied to, betrayed, etc.... But, if these technical issues occur before the ballot has actually ended, then Sakurai can simply find another requested character to add as DLC instead of the other one, and it won't be as big of a deal since no announcements would have been made yet. He wouldn't be going back on something that was officially announced and promised for the fans.
I dunno, just a thought.