Oh boy...this was kinda the opposite of what I was trying to avoid with that other thread...
Wally was never really much of a main character. A great character, yes, but not a main. In the games you only had to fight him twice (not counting rematches post-game) and he never got a starter Pokemon. In the RS arc, even if he did wake up Rayquaza, he still didn't get much spotlight compared to Ruby and Sapphire. He didn't face off with them at the end of the arc, which all main characters get to do. (Y'know, all the final form starters attacking at once. While Blue and Green didn't fight Giovanni, they teamed up with Red to take down Zapmolcuno.) There were definitely plans to make him the Emerald representation, but that was dropped since it wouldn't have made sense for him to be at the Battle Frontier. In any case, yes, netkun doesn't consider him a main character.
It's a bit trickier with Bianca and Cheren. For what it's worth, I don't think even the mangaka is sure whether or not they count as main characters. He broke their Pokedexes to prevent them from getting them and is probably waiting for the new story elements in the inevitable third version to come in before he decides what to do. I don't really think the netkun site really proves their main character status as they don't have their own pages; they're just part of Black's. Starters alone don't make a main character here; the old lady in the FRLG arc has all three Johto starters, Tucker has a Charizard, and a whole bunch of Galactic arcs have Charmeleon and Combuskin.