Those bug fixes get back-ported, and the bugs fixed may have been introduced in versions of systemd released after whatever got included in RHEL/Debian. Speaking as someone constantly frustrated at the glacial pace at which RHEL and Debian-stable update themselves (which is admittedly a feature), it's nice to see them adopting somewhat modern stuff when they make major releases (if systemd v208+backports could be considered modern).

All kind of software has bugs, even 30-years old stable software has bugs. The fact that developers are actively working on new releases, features and fixing existing problems shouldn't stop the software from being in stable distributions like Debian or Redhat.