Who is going to be the neutral arbitrator who assigns Dewey Decimal numbers or Library of Congress codes to web pages? Can’t trust the page authors that’s for certain.
No one. Remember the big list of cool blogs that were generated off HN a couple weeks ago? That's one curated dataset. People can start their own curated databases and then see if others find them useful. Big ones become well-known, like big libraries. Small ones might become known for having the best resources for niche subjects.