Many of the users I have come across doesn't even know what FTP is or how to install or use an FTP client. And if they do, they don't dare renaming anything that seems to part of their site installation, even if they are explicitly told to do so by a peer.
But they still have managed to install a blog, by their web host, by friends or professionals. You could then say they should go back to them for support, but they come here.
The the argument that they may not be ready to self host also goes for upgrades. Should anyone be able to upgrade core and plugins by FTP? If so, then why have WordPress made it simpler?
I really think this is a good idea. It will also make it easier to actually help those users through the support forums.