It’s one of those things that they will pribably get around to eventually, but have a lot of other things ontheir plates first
Currently you as the admin can configure this by hand of course (even on a server wide basis) by editing /etc/httld.conf but the easiest way for a user to do this is with a .httpaccess file so they don’t have to edit any config files.
This is nice for the people out there that don’t know how to use other means to custimize them.
I agree, in the meantime I’d setup default error documents in your main httpd.conf (i.e. 404.html) so that any client who asks you can simply be told to upload a 404.html into their directory and it’ll work.