This isn't about being punished for not following rules or vows. According to tradition, there weren't even any rules in the beginning, but they developed in response to the growth of new recruits. This is a statement about the gravity of the situation for a monk specifically. To live a celibate monastic life is to be extremely sensitive and also to have an abusable power over others. Sexual misconduct is particularly dangerous for someone in a position of spiritual authority.
The example is extreme because it is meant to put the problem into context. Everyone can immediately think of someone harmed by religious sexual abuse, but the idea that it's the context of the sex and not the sex itself is still difficult for us to understand because of our preconceptions. Buddhist morality always focuses on intention and context. The rules for monks and lay people are completely different for a reason.
The example is extreme because it is meant to put the problem into context. Everyone can immediately think of someone harmed by religious sexual abuse, but the idea that it's the context of the sex and not the sex itself is still difficult for us to understand because of our preconceptions. Buddhist morality always focuses on intention and context. The rules for monks and lay people are completely different for a reason.