Backward compatibility

As described earlier, mobile applications need to be working on new and old versions of operating systems. Just because you've developed new versions does not mean people on older versions are not your responsibility anymore. As it turns out, the majority of people who use older versions of operating systems don't download the latest updates. App developers have to use the latest features in new versions of the OS and at the same time they should make sure apps run perfectly fine on older versions as well.