Changing a Book After Its Published

Some authors, based on reviews and suggestions, change a book after it has been published. I'm not talking about fixing punctuation, grammar, typos, etc. Those are changes that should be made. I'm talking about plot changes, rearranging paragraphs, even deleting entire characters.

To me, that just seems wrong. It's like when George Lucas started messing with Star Wars in his "Special Editions". Adding deleted scenes is one thing. I think it would be cool to see a section in the back of a book of those scenes, maybe with little notes throughout the book telling us what page the scene is on. But changing plot lines, deleting/adding sentences throughout the book, stuff like that, it makes me uneasy.

So what do you guys think? Should a book be reworked to that extent once it's been published?