It might be that the Karma system here depends on the validation of the user by the community. HN might keep a score of how many upvotes other users have given

It might be that the Karma system here depends on the validation of the user by the community. HN might keep a score of how many upvotes other users have given you and not allow your upvotes to count until you hit a certain threshold. Account age might be taken into account to limit new ones from upvoting each other for to grant privileges.