The thing is only demos have the save option available, and it's only provided by Dashingdon (Now CoGDemos), not CoG. The final game which is later released by HG or CoG never has it. I think it's because they think going back to a previous point isn't how these types of games are supposed to be played. Like, if you make the wrong choice you should just go along with ir because it's how it's meant to be. Like you said, for replayability purposes.
This is just my guess, of course, but if it's true, I disagree with them.