I'm sure Sakurai has accepted Miiverse as an accurate source for information over a Smash site, or anywhere else, when half of the users don't even know what constitutes a workable character.
Still though, I wouldn't use it as an accurate means of popularity, given the disproportionate number of people who have WIi U's (although there's probably a much larger base in the past month or so due to the 3DS Miiverse. However at this point if this roster isn't finalized, I'd be shocked, so it matters not too much.)