(Poor ridley fans, they must not be real people then by that logic)
Ridley wasn't as popular as many other Brawl newcomers. He was behind Sonic, Diddy Kong, King Dedede, Wario, and was pretty much on even foot with Olimar and Meta Knight. I can't remember how well Charizard did, but I can imagine he would be harsh competition for Ridley too. He was also under Geno, but we all know how well that went.
He was a popular choice, but not in the super league, only after a good chunk of newcomers had been announced. Furthermore, if Sakurai worked out the roster from the Melee polls, then it's a no-brainer Ridley didn't make it in, considering he was hardly requested at all at that time. Even then Ridley did get his due recognition as a boss times two.
As for Palutena, I'm counting on her being in, but I could see her being an unlockable character, thus being revealed only very close to the release date, or maybe even after the release date. For some reason she just strikes me as such.