From the github thread about the urlstore: 

>>If I understand what is going allows storing a url in place on an actual object. When it comes time to retrieve the object the URL is fetched instead. I can see how this can cause all sorts of problems, not the least of which is that URL can be very unstable and there is no guarantee that the content will stay around. Retrieving the content could also be very slow.

>This is designed for cases where the user controls both the server and the IPFS node. Basically, it's treating a remote HTTP server as a filesystem.

Specifically, the internet archive needs this so they can serve their files over IPFS without moving their entire infrastructure over to IPFS.