Which isn’t helpful if you’re a person who doesn’t want to read old posts.
I can only assume "old" pages are down-ranked more by Google than those with no date at all.
Maybe the content date is in a metadata tag somewhere, I've not bothered to check yet. But if it is why not make it visible on the page as well?
What qualifies as a major change can be subjective at times: there have been controversies where newspapers change an inaccurate headline without notice and larger controversies where there is a "stealth edit" that many readers believe should have been publicized. But this expectation that there should be transparency with edits should be the norm.
I believe that articles on personal websites and blogs can only gain by following the practice, too, as it's an indicator to the reader that the author cares about transparency and accuracy.
Located at the bottom of the page.
Typically if a page is no longer relevant but recently updated (like this page was), it would be denoted as such right up top.
They could have rebuilt the page with a new template or something. knowing the original pub date is kind of important for placing the decision in context.