It's really not a wrapper around indexeddb at all. It doesn't even communicate with indexeddb except to save and load data for storage and that is optional. The main use here is for allowing web app developers to be able to load a dataset from a server and then query it dynamically on the client-side, as well as display that data automatically via data-binding.
But that is the point... you don't have to store it in an underlying browser db. It runs as an in-memory store if you don't use an underlying engine. The persistence module is an optional extra and doesn't even need to be included in the library.