Either way, www.example.com and example.com can differ in terms of IP address, underlying hardware, actual website content, and probably other things I don’t know. They are different URLs. It seems problematic to assume they are the same.
Not at all. People already assume they are the same. And they have for 20 years. Nobody reasonable serves up different content on the two URLs. Anybody clueful redirects one to the other. The only reason they're separate is that a) the web wasn't dominant when it was introduced, and b) technology of the time made it hard to manage traffic in ways we can now.
The 9th comment is explicitly described as "bad results"; it's about somebody who doesn't have a redirect. So that for me is in the "unreasonable" category.
The 3rd is about pool.ntp.org, which is a random ntp server, and which shouldn't be serving up web content. They did happen to pick www.pool.ntp.org as the URL for the docs on the NTP Pool Project, but if "www" never was a thing, the would have happily picked something else. E.g. poolproject.ntp.org or ntp.org/pool/ would have been fine.
