Well, when people are deciding at first what software to use, they have varying criteria. Sometimes they just use what's presented to them by default on the computer. Sometimes they have a whole list of requirements and they do lots of research and pick the software that has all the features they need. But once they've picked a program, they will stick with it unless there is some compelling reason to leave. It's not like people constantly are looking for new software to replace yours – they only start looking when your software just won't stop sucking.
As long as you consistently suck less with every release, you will retain most of your users.>
You're fixing the things that bother them, so there's no reason for them to switch away. Even if you didn't fix everything in this release, if you sucked less, your users will have faith that eventually, the things that bother them will be fixed. New users will find your software, and they'll stick with it too. And in...