At least HN karma is incremental and based on something approximating merit as opposed to being a slot machine where you never know which comment will earn Karma. More effort or rare insight, generally yields more karma.
That doesn't make it any less addictive or manipulative.
That hasn't been my experience. How much karma you get is heavily dependant on how many people see the comment. The most insightful effort-filled comment at the bottom of a 4 day old thread isn't going to get you nearly as much, if anything, compared to a joke with just the right amount of snark at the top of a post currently at the top of the front page.