I would argue that at least at the time that webpage was written and maintained, none, of them (including the standard) got timestamps right. In the above case

I would argue that at least at the time that webpage was written and maintained, none, of them (including the standard) got timestamps right. In the above case timezone is actually an offset. Arguably, timestamp with timezone should store a timestamp plus a tz_database time zone. Storing offsets is easy and useful but not necessarily correct. Timestamp with Offset should be a different type. Validating all of those rules would be a hairy mess. For example, what do you do with a timestamp in the future when changes are introduced (negative leap seconds, changes to DST, geopolitical changes affecting timezones).