Android's APIs enable easy implementation of a sqlite-based data model, where changes are always persisted.
That doesn't solve the problem for things like CAD that need an in-memory object-oriented data model, but the Android support for observer patterns can be wrapped around any data model, and the ability to quickly, which means, in practice, incrementally, persist changes is driven by both Android-specific issues like needing to respond to lifecycle events quickly, and by general mobile considerations like a battery that could fail unexpectedly.
In other words, you need to solve the "don't explicitly save" problem for reasons ranging from "it's more robust" to "it fits Android UI conventions" anyway.
