Seems like the same basic issue as http://meta.ubuntu.stackexchange.com/questions/47/how-do-we-tell-if-a-question-belongs-here-or-rather-at-stackoverflow-superuser
It simply depends on the question.
Any basic question where the answer involves point the user to /etc/apache2/sites-{available,enabled}/ or /etc/apache2/mods-{available,enabled}/ feels rather specific enough for this site. On the other hand, to continue with an Apache example, a question comparing the benefits of different MPM:s (prefork, worker, etc) might do better at serverfault.