Johnny Novgorod said:
If the voice is well cast then I don't care whether the person behind it is famous or not. To stick to Kingdom Hearts: I suppose the Disney voice cast are celebrities among certain people, but then who else would you cast in the roles of Mickey, Donald and Goofy? And Haley Joel Osment's a celebrity but all you get from his voice is "hero kid" and that's fine. On the other hand you get people like Billy Zane or Christopher Lee and, while their voices can be very sexy, do they really fit their characters?
Well there are back up ones for the Disney cast and characters. Genie wasn't voiced by Robin Willaims, but instead he was voiced by Dan Castellaneta. Currently there are also 2 voice actors for Mickey Mouse now, the first one being Bret Iwan who will be the voice of Mickey Mouse in Kingdom Hearts 3 since Wayne Allwine died, and the second one is Chris Diamantopoulos. They also are probably searching for a new Scrooge McDuck voice and or a possible new Ursala voice since Ursula's voice actor, Pat Caroll, is currently 86 years old (she's voiced Ursala in every appearance, including Dream Drop). Meanwhile Scrooge McDuck's voice actor, Alan Young, is currently 94 and is still voicing the lovable greedy duck, with his last full voice over being in the Ducktales HD remake release last year.
As for the Kingdom Hearts created characters, I was surprised by the fact that Mark Hamill, the Joker, voiced Master Eraqus in Birth by Sleep. Hell Master Xehanort (Old man) is voiced by Leonard Nimoy in the English version and was specifically chosen by Tetsuya Nomura because of the fact that the played Spock. Heck, Master Xehanort's Japanese voice actor is Chikao Ohtsuka who has been the voice of Dr. Eggman since Sonic Adventure 1 and voiced Captain Hook in the Japanese dub of Disney's Peter Pan. Another interesting thing is that Akio Ohtsuka, Chikao Ohtsuka's son, is the voice actor of Ansem Seeker of Darkness while also voicing Blackbeard in the One Piece anime.
This nerdy voice acting trivia has been brought to you by a Let's Player who generally researches who voiced who in the LPs he does. XD