I think the fundamental difference is HN started as Graham's dogfood and Reddit was began as a startup. A subreddit might solve someone's problem, but to a fir

I think the fundamental difference is HN started as Graham's dogfood and Reddit was began as a startup. A subreddit might solve someone's problem, but to a first approximation it is never solving the problem of the person who coded it up. It is not a Reddit software engineer's passion project.