And how do you think any other website decides what to recommend you, if not other users' actions? Remember the Netflix prize? The data set they gave you is how other people rated movies. You can absolutely build a recommendation system without manual input from the operator.

And HN absolutely does promote submissions at the moderators' discretion. The moderators sometimes give old but overlooked submissions a second chance, they also turn the flamewar detector on some stories that they think deserve more attention which effectively promotes them against users's will.