Yes exactly. The iPhone apps are a lot better since each version of the phone has the same camera (all iPhone 5's have the same camera for example). There's like 20 different Android phones out there each with a different camera so making a good App is harder.
Though I am not an Android developer, I can think of a way around this... Provide a special "calibration" mode. The user could enter the calibration mode, point the camera at a gray card under sunny-16 (or sunny-11) conditions and hit a button. This could then be stored as a setting for the app on the phone. Presto... Calibration complete - at least in the linear response range for the camera.
Shoot more film.
There are eight ways to put a slide into a projector tray. Seven of them are wrong.