I agree that in many instances estimating the life expectancy (from the customer's viewpoint) is difficult but in others it can be reasonably straightforward. I

I agree that in many instances estimating the life expectancy (from the customer's viewpoint) is difficult but in others it can be reasonably straightforward. In the software instance that we offer free upgrades for life we are clear that our customers anticipate building and maintaining a body of data over very long periods of time - they select our product because they are persuaded both that our software meets their data recording needs AND that we are going to be sticking around maintaining that software long into the future.