On SE, deletion of posts isn’t permitted, perhaps outside of some extremely exceptional circumstances†. Once it’s posted, it becomes part of the community.
Yes you still have the copyright to your posts (where applicable) and yes you can post them elsewhere, turn them into blog posts, write a book, whatever. But the post on SE becomes the community’s. And if there’s something missing from the answer, it should be edited into the answer.
(as an aside, I’d quite like the ability to upvote edits, for those folks who turn other folks’ lump of iron Q or A into gold, but that’s a feature proposal for elsewhere)
I agree with @gilles that the example comments you provided should be part of their respective answers. The goal should be to build a network of high quality QA; the information required should be in the post itself, not in a comment, discussion page or note.
As a supplementary point to that, a post author should not be able to block critical/relevant edits to their post.
Editing posts is mostly separate to reputation, and can be done with a model like SEs, something slightly different, or another system entirely.
†: Exceptional, like: “We’ve posted the code to the Vatican’s health system and it contains the Pope’s medical records!”