There is no way a character like Geno would make it into Brawl. He is overrated and doesn't even fully belong to Nintendo. He was a support character from an old Mario game and would probably never come up in a Nintendo franchise again. Uh, he was the only original character from SMRPG that even appeared in another game in some form. He makes a brief cameo in Mario and Luigi: Superstar Saga but even that is more then anyone else has. Really, the fact that people still like him and still want him to reappear in another game after 12 years of not having a playable role is pretty significant. Really, it that matter, how is Geno any different from Pit?Even ROB is more deserving than him. ROB didn't deserve jack and the reason for his addition was to be nothing more then a WTF character. Really, Sakurai made the roster in the course of two days and quickly chose ROB when he found out that there really wasn't anyone else that could genuinely fall on this level besides Mr. Game and Watch. That's all there is to it.
Back on Topic: Jigglypuff may have lost her importance which is ironic because she never truely had any, but popularity and moveset are probably the main reasons she's in besides being one of the original 12. She is as WTF character with a unique moveset that can't be replaced by any other Pokemon/Nintendo character.
I do agree that characters like Krystal and Ridley should be in Brawl, but they should not replace such a valuable member of the Smash cast. Instead, characters like Wolf or Falco should have been replaced by Krystal and Ridley/K Rool. Not only are they clones, but they are too conflicting... Fox fans do not like Falco, Falco fans don't like Wolf, etc. Krystal would have been an amazing and unique character being able to weild staves and magic. She's also a female... but I'm getting off topic again.