Wilson score confidence interval is easy to implement and already proven to work greatly on Reddit, where it is the default sorting algorithm. Do note that Reddit also has down votes and Reddit also has threaded comments. While I agree, it's not the "perfect" solution, but for a perfect solution HN admins would need to invest a lot of time (and it would probably be a lot more buggy and in the end they probably won't come up with something that's better). Going with Wilson they can do a quick fix that would improve the sorting a lot.