With Kickstarters it's explicitly laid out that "if we make x amount of money, y and z will be in the game", how much they made over their basic goal really isn't relevant since this is for completely different features.
That being said, yes it's greed, of course it is. So is making the game to begin with, honestly.
Obviously a smarter dev would instead just overestimate the required money for everything and then come out later saying "look guys, we made this extra stuff for the fans too" and make it seem like they were being fan-friendly, but oh well. I'm just not going to bother donating since I don't care for English voices. I just wanted the game to be made, don't really care about all this extra stuff.
Although really, you'd think an English voice cast would fall under the creation of the game, especially if there's already going to be Japanese voice acting. Inafune took the project to Kickstarter and I'm sure he knew he had lots of western fans so the fact that he's asking extra for a full localization is pretty lame.