As per the article, the quality of content is moderated by editors who patrol the edits frequently. For example, you can go to a random wikipage and make some i

As per the article, the quality of content is moderated by editors who patrol the edits frequently. For example, you can go to a random wikipage and make some insane edit right now and there is a good probability that it would be reverted within few hours. This probability decreases over time when number of articles doubles but editors patrolling them decreases. Eventually you will start seeing lot of low quality edits sipping in and stay there for very long time.