nobody would really care if some particular machine stopped serving some particular file. Yes they would. Because such systems can only serve files that exist

nobody would really care if some particular machine stopped serving some particular file. Yes they would. Because such systems can only serve files that exist on at least one node, people who want to rely on such a system to serve a given file must run their own node to host every file they care about the availability of. The topological properties of distribution are different, but the existence of the local cache to provide dependability is not avoided.