This exception was added to the guidelines when it was common practise to have many of the Fedora specific tools not available as a source release separately and the only way to get them was to extract it from the source rpm package. However this is not a sane development practise and hinders cross distribution adoption and participation. Therefore, it is much better to drop such exceptions and recommend a proper infrastructure instead. This exception is just historical baggage left over from the early days and reducing the length and keeping the reviews more straight forward for future projects is a added advantage.
A while after system-config-printer was adopted by other distributions like Ubuntu and Mandriva, there was a specific request from another distribution that they prefer dealing with a tarball and proper SCM management for similar tools rather than having to extract the source from the tarball. We did not have proper hosting facilities within Fedora and delayed this. It is high time we demonstrate good upstream project practises (tarball + patches in cvs is just not good enough). The fact that not all upstream projects do this yet is not a good excuse.