The third one isn't meant to imply that you should keep adding needlessly, or that you should necessarily add more functionality (yes, this is how feature creep starts). It's meant to indicate that software is never truly finished: there is always something to fix or improve upon (e.g. refactor).
It's perfectly fine if you make the conscious choice to not make those fixes or improvements, usually for time/budget reasons, but the point is that you should be aware of those possibilities, and that those are the points to revisit if and when you have the resources to do so.