Random memory: MIT’s web site
I remember that when I first got onto the Internet, MIT’s official web site was at web.mit.edu, while www.mit.edu was the students’ association or something like that: certainly associated with MIT but the site wasn’t the main MIT web site.
Now, though, both URLs show the same web page. I suspect that nowadays, when people guess at URLs and type them in directly, rather than following links (as was envisioned in the early days of the Web), having a main site that is not at www. is simply not viable.