Assuming you are talking about lock-step updates of firmware and app, how would an app work with firmware lagging hardware, or updated firmware but old app?

People have multiple devices (eg tablet and phone) which means they'd easily get into such a state.

I imagine they have to keep the most of backwards compatibility for their internal purposes as well (or at least their developers' sanity :)).

I am pretty sure having open APIs (that evolve) would still be more appreciated than not.