Then you really should use something like SVN or GIT to make diff of the changes of each update. Personally I use SVN for this. This in combination with the changelog is more then enough. Most changes are mentioned by having "(SKINS)" in the heading of the changelog, like this entry: https://directadmin.com/features.php?id=2381
I would not wont to expect more then this. I don't want DirectAdmin to use more resources then they already do, to describe ever little code change. Just read https://directadmin.com/versions.php thorough before updating, and then use SVN to track every details of the changes.