It's pretty easy to ask permission ... for a copy of a fic that's been archived with still current contact info or under a pseud that leads to a website with current contact info when you search for it. I wouldn't want to hazard a guess on the percentage of stories at 852 Prospect or Heliopolis or Area 52 or an XF archive or a popslash archive or an old dS archive or, well, basically any fandom older than about two years, for which that would not apply.

And I would think that the reason you would want to record a fic, either from an untraceable or disapproving author, was because you wanted to record that fic, in the same way that I write June/Neal instead of (Elizabeth)/Peter/Neal in White Collar, because I'm interested in that scenario more than the one that would garner lots of comments fast. Or even more basically, why people choose to make fan works instead of imagining everything from 'scratch'?

Stories aren't fungible.