Personally, I think that moderation transparency is a noble goal: I'd be in favor of all forums keeping explicit, public moderation logs with all moderator actions. But then again I have never had to moderate a particularly large forum, so perhaps my opinion would change when forced to deal with the same spammers, day after day.
I agree with you on moderator transparency. There should be a certain amount of it visible to all, and that amount should definitely be more than what's available here on HN and Reddit.
Reddit is far worse, because you can be banned for arbitrary things without recourse, even though it's theoretically against the site moderation guidelines. You can be banned from one subreddit simply for participating in another.
I don't think HN has the same degree of problem, but I think the solution is the same. Sometimes, sunlight really is the best disinfectant.
There is, in fact, research showing that this is how it works on Reddit: users who get told why they're being banned or their post removed go on to be better contributors than those who don't. I can dig up the paper if you're interested, but I don't have it on hand.