Exactly, many don't seem to grasp this, not much difference here to how banks just 'make up numbers'... what's preventing them from selling you coins that don't exist... you'll never know until you try to access them
That's why you need more than just a database to do this right - you need a cryptographically-secure accounting system and verifiable auditing.
That's Open-Transactions.
Anyone who wants to solve this problem is going to have to reinvent all the work they've done, and they have a head start. All OT needs is add a few missing pieces to handle the bitcoin side of the equation and they'll be done.