Even the most nominal employee calls in sick when they can't show up for work. To do anything less is grounds for dismissal, and rightly so. A business could never operate effectively if the employer had to guess who would show up on any given day. While the job aspect of the church is important to these folks, I believe they pre-report their absences for another reason, a far more significant reason. For these dear folks, church is not merely a social institution.
Church is family.
The people of the church are those with whom they share their lives. For them, it would be insensitive and rude to leave town without letting family know. At almost any given moment, I can give you the approximate whereabouts of my family members. We constantly report to each other because we care about each other. If one of us goes out of town, all the others know.