But you can encode fulfilment into a smart contract for physical goods, assuming that those physical goods have some digital representation on-chain. Discrepancies between the chain and the real world continue to be resolved through the court systems in various jurisdictions, but on-chain activity is just strong evidence that any court can rely on.
> a distributed ledger only has value over and above a non-distributed one if other parties worry about the centralised database manager tampering with records
An alternative viewpoint is that a centralized database manager can be seen as a potential risk. One of the general ways we progress in society is when we reduce sources of risk, and a permissioned blockchain where you need 2/3rds of a cabal to collude is a pretty clear reduction of risk compared to a centralized DB. (I mean, how would you keep track of whether a central DB has been tampered with? You'd probably maintain your own copy, reconcile the two periodically, and flag discrepancies if and when they happen. That's exactly what a blockchain is.)
To be clear, I'm pretty skeptical about blockchains in general, but this seems like a very compelling use case.