A bit of an off-topic: the real WTF for me is that there is such a thing as a save button. I cannot fathom that most software requires us to perform an ancient ritual lest they throw away our hard work.
[1] - Yes, I could hit the undo button repeatedly, since any editor worth its salt will have a virtually-unlimited undo. But it's reassuring to know that you've undo-ed to exactly the right point--in Vim, at least, the "+" indicating a modified file disappears once you've undone all your changes.
If we were to do away with the save button, the rest of the “working with files” story would have to be thoroughly rethought.
If I'm using a word processor that is automatically saving, why should I have to then explore my hard drive to find the file and examine previous versions? The app I am using needs to present this interface (even if it is ultimately supplied by the OS, like save dialogues).