Please remember that Android is an offshoot of LINUX which means no matter where the storage is to the operating system (Android) the save location is only a path. If you have an SD card it will be mounted in to the operating system. On Samsung devices in fact internal storage is treated as an SD card and so is external storage and it is mounted accordingly by the operating system. So from that perspective there is no restrictions of where you write, it is simply the decision of the developer on how to handle the writing to the OS. In fact you can see that clearly if you are a developer and have the phone connected to your laptop, everything is a mount point from root.