why would the ability to do it automatically necessarily change that set of assumptions?
I tend to assume an official, endorsed feature works better and more smoothly than something I juryrig tediously by hand. And if I had a feature for saying an entry is only public for a short time right from the posting, and the systems knows this, I assume it is different from an entry that the system assumes to be permanently public without any inkling that it is supposed to become private, and then change that afterwards, when the system can't do anything anymore about having featured it in RSS feeds or whatever.