Reddit's system works that if a post get 1000 upvotes and 500 downvotes (66% liked), it will be scored worse than a post than gets 10 upvotes and 0 downvotes.
Basically what it does is penalize controversy, which is the perfect decision for a website that is about mining the most humorous and widely-liked response.
Anything that is 51% liked and 49% disliked (e.g. political individuals mentioned in a non-political thread) gets bombed to the bottom almost immediately, which is exactly what most redditors want.
The other brilliant thing it does it let the user adjust this prioritization if they so desire.
Reddit's system encourages purity spirals, especially when the main topic of discussion is how terrible everyone else is.
Downvote-based systems are better at having the consensus viewpoint and quality content bubble to the top, at the expense of pummelling some of the dissenting views.
Upvote-only systems seem to have worse stuff bubble to the top.
Ironically, it doesn't affect me at all on Reddit. I have such low expectations for the platform that I don't even notice my own karma score nor do I bother to look at posts of mine to see how they're being received. HN makes your score much more prominent so it's easy to see it moving and you know immediately whether you've said something controversial somewhere.
1. Comments cannot fall below -4 points
2. Downvoted comments only get greyed out, not hidden entirely
3. Most topics on HN are not political (though there are certainly exceptions)
4. The community here is (usually) a bit more mature than on other sites like Reddit
[1] Often, the assertion "this topic is not or should not be political" is political. Because politics is how we organize society on a large scale and saying things should be exempt from that, guess what, is a political opinion.