Why does gvim read /usr/share/vim/vimrc instead of ~/.vim/vimrc

Question

:help startup states, under 3. Execute Ex commands, from environment variables and/or files that (for Unix systems) $HOME/.vimrc or $HOME/.vim/vimrc is read and that The files are searched in the order specified above and only the first one that is found is read.

I do have a (read/writeable) ~/.vim/vimrc file, so I have expected this file to be read first.

However, when I start gvim (debugged with the -V20 flag) I see that gvim first reads /usr/share/vim/vimrc. When it is finished reading this file, it then reads my ~/.vim/vimrc file. I don't want the /usr/share/vim/vimrc file to be read at all.

The environment variable $VIM is not set.

Interestingly (and somewhat surprisingly for me): after gvim is started up fully, :echo $MYVIMRC prints /home/rene/.vim/vimrc.

So, my questions are: why does it behave differently from what is stated in the help file and how do I make sure that only ~/.vim/vimrc is read.

Answer 1

Reading system-level configuration before user-level configuration is totally normal and expected in UNIX land.

Anyway, this sentence:

The files are searched in the order specified above and only the first one
that is found is read.

only applies to "personal initializations".

As explained a few paragraphs below, the system vimrc is read no matter what:

b. For Unix, MS-DOS, MS-Windows, OS/2, VMS, Macintosh, RISC-OS and Amiga
   the system vimrc file is read for initializations.  The path of this
   file is shown with the ":version" command.  Mostly it's "$VIM/vimrc".
   Note that this file is ALWAYS read in 'compatible' mode, since the
   automatic resetting of 'compatible' is only done later.  Add a ":set
   nocp" command if you like.