I didn't say anything about git. I said the commit messages are eternal, and none of those changes will change the commit messages (except, perhaps, changing the VCS, but usually that will preserve commit messages too).
You'd be foolish to do a VCS migration that discards the commit messages. I've never seen it happen personally, as people tend not to be that foolish. I've worked with legacy codebases that went from CVS -> SVN -> git and all of the commit messages going back to the very beginning are intact, because why would you ever do a migration that doesn't maintain them?
