> The reason for this is that a forum is a collaborative effort, a collective work, and the contributions of other people's content might only make sense in the context of yours.
Sure, but what about posts that have no replies? And what about a cascade, that is, poster B replies to poster A, poster A deletes their account, the post remains, poster B deletes their account, both posts disappear?
I don't care about HN or Skype as much, but when I get my commenting system done I will look into doing something like that. I do believe in letting people and their content go. It's like making a party: yes, if people start leaving the party will be less fun, but it's more fun that way for the people leaving, and the rest ought to cope; considering one day they might want to leave as well. And while link rot sucks, so does everything just growing and only growing all the time. Let the web be a jungle, a living thing, and let things die, too? In the tiny part of this garden I attend to, that's how it's going to be. If in doubt, it's a zen thing ^^
At any rate, I don't really see the "liability nightmare", since it's already a fact that if you post something on a forum for 5 seconds, someone could take a screenshot and reproduce it until the end of time -- liability remains with the people posting stuff in the first place. It's just a matter of politeness to reduce this as much as you can on your end for anyone who wants to take something back, to do your part, without that implying any promises -- the way I see it, you loose some content, but you gain other content, because people know it's not necessarily etched in stone, and can try themselves out.
Again, I'm not complaining about how any site handles this, and I'm happy to post on HN. But Plutarch said the mind is a fire to be kindled, not a vessel to be filled, right? Likewise, I believe in the process of the web much more than any heap of "content" it might produce. And at least for what little own content I have on my site, I intend to curate it every now and then, check for broken or obsolete things. I'm not even above editing year old blog posts, the whole point is that should I die, I will leave the best of what I made and thought, not just an endless "log" like toilet paper. If in 10 years some of what you wrote today doesn't strike you as silly and outright false, what did you do in those 10 years?
Public spaces like HN and reddit and slashdot I feel are different from that -- you get a lot out of them, and for that you give up "exclusive ownership" for what you said. This is fine, but I could see that a private or small community might feel similarly like I feel about private things; they don't exist for the sake of historians or lurkers, but for what they have with each other. When that ends, there is no need to keep it around. What does it profit a person if they gain all the content of the world, but lose their ability to reinvent themselves, right? Not everything is a wiki, not everything has to be revision controlled, not every conversation is about timeless facts, or facts at all.