> but will make it so the address the item is stored at returns nothing
There's no way for the blockchain to do that. The only way this is possible on ethereum is if the smart contract includes a self-destruct function, and the owner of the smart contract decides to call it (either because their private keys were compromised, or because they were coerced into doing so IRL). Otherwise, it's technically impossible to do without taking down the entire network or breaking encryption.
I'm less familiar with IPFS so can't really speak much to that -- but from what little I understand, censorship-resistance is also a major selling point there.
> So, it's the equivalent of some entity controlling the DNS?
There is the ENS, but even then, nobody can take an ENS domain down except for the owner of that domain. Not even the creator of the ENS smart contract, unless they specifically included upgrade functionality into the contract, because smart contracts are immutable.
> Sure, the item at the address is immutable, but you might not be able to get it.
As long as you have access to a single Ethereum node, or access to a service that has access to an Ethereum node, you will be able to get at it. It's hard to imagine you not getting at any Ethereum nodes unless a Great Firewall of China situation exists, and even China doesn't care to ban most proxies.