It doesn’t use anything. /etc/mtab is a symlink to /proc/self/mounts and gives you the parameters for mounted filesystems. Some of those options are defaults and are as such not required to be explicitly set in /etc/fstab.
Wrong way of thinking. You’re trying to think of this with the mindset of a Windows user, while GNU/Linux is a UNIX operating system. Windows was initially conceived as a single-user GUI for DOS, a single-user operating system. UNIX is a multi-user system and makes extensive use of permissions.
The following two tutorials will make everything clear to you.
