That's pretty hand-wavy. Anyone can read the published code, but you can't read the code being run by each individual entity in the network. Any individual might change their server to not make the stored data available to those paying for the storage.

It's not _likely_, as that would negate the usefulness of the whole system if it became an issue, and therefore negate the cash flow into the system.

Ultimately what's keeping the storage providers honest, whether they're centralized or decentralized, is that their future profit stream is based on their current behavior, and they presumably care about future profits. Code and SLAs ain't nothing but words.