The funny thing is that the Internet as searched by Google is organised hierarchically. It's just that Google exposes it through terms produced by their indexing activity. And when someone wants to access a specific resource, and especially update such a resource, they typically don't navigate to it by trying to fish it out using a combination of search keywords. It isn't a matter of "scp article.html editor@[linux,news,lwn,latest]" and hoping that it connects to the right place.
One can argue that this hierarchical organisation is imposed by physical constraints and that beyond the first level, one could use tags, terms, categories or whatever just as successfully as a path to a particular resource, but the issue is convenience for the specific task being performed.