Mrs. Rowling has left us with a mass of contradictions when it comes to Gringotts. Making sense of it is practically impossible, and yet necessary to fill in many of the plot holes surrounding Harry.
How do vaults work? What kinds of vaults are available assuming vaults differ by more than just size and the nature of the protections surrounding them? What other services does the institution offer? What is the relationship between the bank and the Goblins as a whole?
Speculations
- In "Inheritance" of Tales From the Cutting Room Floor: Harry Potter, EdStargazer offers a view where vaults are, with the exception of trust vaults, just vaults, and thus do just differ in size and the nature of the protections on them. Gringotts as a bank does offer other types of wealth management services, and outside of uninventoried household furnishings, the bulk of the Potter wealth is invested in such offerings. However, at this time, it generates little more than is needed for Harry to live off of comfortably but not extravagantly.