Pushing a new timestamp to a list for every edit/resubmission makes me more comfortable, and keeps the immutability aspect (a trustable record of history).
I'd also prefer being able to see the full edit history of comments, so assign weights to my views accordingly (a grain of salt).
I should add, for anyone who hasn't read the post I linked to above, that the original timestamp is always available from the user's /submitted list (linked to from their profile) and the /from list for the site (linked to from the domain name in the title line for a story). The relative (re-upped) timestamp is only shown on the front page and the /item page. Over time, the two converge, since the re-upped submissions to date have all been recent, i.e. less than a day or two old.
The intention is definitely not to make the original timestamp (or any other information) unavailable, and we'd be happy to hear suggestions for how to handle it differently.
Showing the history of comment edits is another matter. Sometimes people post things that they shouldn't post, and it seems decent to give them a way out by deleting the comment or editing out the sensitive or egregious bit. I think that's a fair privilege to trust users with—it's part of having a real community and good conversation, and although a few do abuse it, it really is surprisingly few. Except for a few perfect souls, we all blurt out things we shouldn't, so we all benefit from this. And we'd hate for bad real-life things to happen to people over what they post here.