There must be some software analyzing comments based on different parameters (length, downvotes, scans of problematic words/phrases, and more...machine learning/AI too?) and flagging them in a queue for attention.
Metafilter is another example of a small-ish, highly moderated community that does a thorough job with a small handful of dedicated moderators.
The oldest comment on the first page of https://news.ycombinator.com/newcomments was posted 15 minutes ago. Reading through all of them took me 5 minutes. Ignoring the fact that posting frequency varies throughout the day, reading every comment would require a single person to spend 8 hours a day every day. So it seems possible to moderate HN like that, but I really wouldn't want to be in dang's shoes monitoring the contextless comment stream all day.
Crowdsourced via the flag button, which acts as a "superpowered downvote" even though it's not presented as such.