I think they're all good points, though I disagree with #6. It doesn't steal comments from the source because I would never comment at the source and there's a lot of value in having conversations with people with whom you share a history and context. When patio11 comments on something, I know where he's coming from for the most part already so he can get right to the point without having to give background information I already have.
>>johns+(OP)
I agree with this. Follow up question: I've seen sites where HN comments appear in the source's comments (like trackbacks). Can someone point me how to do this with Posterous?