What is the [ Program in /bin Directory?

The point of -f is to try and avoid the need to stat every file entry, and to avoid the need to read them all before any are displayed. It is a "meta" option that just disables other options.

So, yes, it should do what you expect. I can't answer why it isn't, but I would guess that you might have a shell alias or something else that inserts additional options to the command. That might reenable a feature than -f disables, and be considered "more specific", so take precedence.

The most important parts are the GCC compiler, glibc C library, the coreutils and binutils basic Unix tools, and probably the bash shell and the Gnome desktop environment (if you use those).

Just source line count doesn't take the relative importance into account. If you take e.g. Debian's or Fedora's full software selection, most people don't even install more than a fraction of it. And (unless you are extremely organized), chances are that they have lots of packages installed because they got intrigued, installed it to check it out, and forgot all about it. So not even statistics on packages downloaded (like I believe Debian maintains) is a fair depiction.

Added later: I just came across this page by O'Reilly (with an included poster showing contributions to a Linux system).