Who should be involved in securing a Drupal Site?

A lot of attention is given to writing secure code for drupal. But is securing a drupal site only a matter of writing/using correct coding, or are other roles as much responsible for securing a Drupal Site?

What's the role and task regarding security of:

• A coder
• A developper
• A site admin
• drupal.org
• Endusers
• Organisations