And there must indeed by some central authority giving 'ultimate trust'. This is Zooko's triangle. By default IPNS gives you 'decentralized' and 'secure', but you can also opt to tie an IPNS name to a DNS TXT record, and lose 'decentralized' (at least for the initial lookup) but gain 'human-meaningful'.
Besides, the idea is that IPFS could happily support Namecoin[1], so there's the decentralized, secure, and human-meaningful DNS service. The only 'non-secure' aspect there is the unlikely event of a 51% attack.
Namecoin is merge-mined with Bitcoin by many miners, so if you wanted to 51% it you'd need a pretty large chunk of Bitcoin's hash power. An evil pool could do this, however it would be visible on the Bitcoin blockchain that they were doing it (although not what transactions are present/not present in the attack chain).