I suspect that the software does that automatically on the server. Given that 'cartels' are likely to be automated and hence at web rather than human scale, at least some of the counter measures probably should be as well.
Well those are the flagrant cartels. I hear there are pure-human cartels too. I see emails and Facebook posts and en-masse emails asking for Product Hunt up-votes from time to time from some VC associates. I imagine there is a similar thing going on on HN (but what do I know...i'm just a tiny startup staring at PyCharm most of the day.)
Because it is mostly a site for press release type content, I suspect Product Hunt has less incentive to discourage those sorts of get out the vote activities versus Hacker News. And Hacker News users have more incentive to flag posts that rise for reasons other than interesting content or comments. I mean, if I have an informed expectation of what I will get on the Product Hunt front page and it is different than my expectation about the HN front page in part due to the way get out the vote activities are treated.
