The problem that the blockchain solves is essentially one of decentralised consensus on mutable data. Decentralised consensus on immutable data is "easy" (see Bittorrent, IPFS), but getting everyone to agree on who owns "yoursite.com" and what data it points to fundamentally depends on a universally agreed key-value mapping. Using a blockchain allows everyone to agree on such a mapping, with some nice extras thrown in like blind auctions and public key crypto. Namecoin and the newly launched Ethereum Name Service work similarly.

The big question given the inefficiency of proof-of-work blockchains is whether there are other ways to do decentralised mutable data. I'm currently working for MaidSafe, whose approach is based on a more traditional DHT and voting amongst randomised groups of nodes. We're still in alpha however, so for now the working systems are all blockchain based.