If you want to keep track of the changes made to a node as comments, you can use this module: http://drupal.org/project/nodechanges

1. Install and enable the module
2. Go to the content type you are interested.
3. On the top, there is a tab "comment fields".
4. Add a new field to the comment (not to the content type)
5. Select field type: Comment diff and widget: Hidden
6. Set the number of values to "unlimited"

All of the fields attached to the node are hidden from display by default. You can manage display in "Administration » Structure » Content types » your_content_type » Manage display » Node changes output"

You will now see the changes you have made to a node as comments.