Imagining that were true, you would never be redirected to an https version of a page.
But, there's nothing stopping me from running a webserver listening on port 80 (so, accessed in the browser at http://example.com) that serves a picture of a baseball. I can also run a webserver listening on port 443 only (with SSL/TLS set up, so accessed in a browser at https://example.com), on the same machine, that serves a picture of a dog instead.
This sort of breaks the rules/conventions though because you expect the resource to be the same by nature of the URL you're using to access it. But nobody has to follow that rule
The point of URL is to identify a single address owned by one guy. Removing the www subdomain means you have two addresses, possibly owned by two guys.