Since there's nothing at the moment to stop someone from making an inflammatory comment then editing it to a blank post or a 'sorry, duplicate, please delete', I don't think that bein able to remove the post would add any power in that way. It is nice when people use Update:, but nothing keeps them from not doing it (if this ever became a problem, perhaps version numbers could be automatically included,as demonstrated in this post).

If duplicate and blank nodes couldn't be posted, I agree that it would be rare for someone to want to delete a post. I can't think of an example this morning. However, one way to handle it if it were needed, which wouldn't break threads, would be to simply change the text to "This node has been deleted by <author|admin> [because <reason>]", then add a note next to the title that says Deleted. The body text wouldn't need to show unless the node had been specifically selected.