Most of my side work is contributing to existing projects, but here's the stats for 3 school projects: 20,896 lines deleted for 30,342 written. 2 of the projects had fixed requirements from the beginning though one was a more free-form independent study. Additionally all 3 had only one additional author and I did a majority of the line additions and deletions.
I'm pretty sure these numbers are way untypical for this sort of work---with fix goals and deadlines with no more than a few months per project I assume most people delete pretty little, and basically only during debugging.
Certainly this refactor-happy approach did cause some missed deadlines early on, and getting all the abstractions correct still means basic functionality often doesn't come together until the last minute. But I still that the immense technical wealth does pay off as I get more productive the longer I maintain the project---the abstractions anticipate the sort of extensions I may later wish to add by laying a firm foundation. And the fact that the functionality does appear last second speaks testifies to the increasing productivity---longer hours or last minute panic doesn't explain it.
I think most managers would be horrified this approach, but if you're a real company planning on being around indefinitely and not some startup just hanging together or student, this method should be all the more fitting.