Subdomains can be set up differently at your registar and the www is a subdomain. by default they would be the same, but you can go in and make those changes.
They have different TF/CF cause people sometimes link domains with the WWW versions and sometimes without it. The Domain Name Registration and Web Hosting | Domain.com and domain.com versions are two different addresses, just happens most people redirect one to the other, but people linking to domains don't necessary know if the website is primary www and another is not. Now throw in SSL (https) versions versus non-SSL (http) versions, and you've got a new dimension of variables.