The web used to be a collection of sites, loosely linked. Domain was king.
Google blew up the web. The web became a collection of pages, more tightly linked, and you could find any page you needed.
Reddit and Digg and Delicious atomize the web. No need to read blogs any more. Instead, let others do it for you, and these (and the many other) social news services surface the most interesting, the hottest, the most controversial posts for you.
This satisfies a basic human need… to do what others are doing, to read what others are reading. It reorganizes the scattered threads of discourse, creating a few (instead of a million or a billion) reading lists.
Of course, there will be a million imitators and improvers. And then another generation to synthesize them (a la popurls). It’s not the end, just another beginning.