It's due to different groups controlling different parts of the infrastructure, allowing for separation of privilege -- and is the whole reason www even existed to begin with.

Often these separate groups aren't part of the same organization. They're a different organization or contractor paid to maintain a web presence.

Yes, but those are decisions made by whoever controls foo.com. This may not be a good decision by Google, but I don't think they should be held responsible for a decision that was made by whoever controls foo.com.

This is completely backwards, because Google just made this decision _now_!

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.

> Nobody reasonable serves up different content on the two URLs.

The third and ninth comments in the linked bug present real world examples of this behavior.

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.