The problem with this approach is i.e not owning backend piece, soon your app will need some kind of backend business logic and not just data storage/access APIs. And when this logic is needed you will be left with no choice but to build this on the client, you mobile phone. So if you building for multiple mobile platforms you will have to replicate this business logic across all clients. Not very efficient in terms of cost, developer resources and time. This is exactly the reason why client server technology failed and could never scale.
While this may still work for apps (games may be) that are light on backend-logic, I feel there will be some duplicate work that will still be done if you develop across multiple mobile platforms.
Not sure how other folks feel about this.
