About Drupal 7's permissons
A straight grep for the full string may not find these, but they're used. For instance look in the modules/node/node.module, where you find calls such as:

if (user_access('edit any ' . $type . ' content', $account)
  || (user_access('edit own ' . $type . ' content', $account)
  &amp;&amp; ($account-&gt;uid == $node-&gt;uid))) {


Note that the string is constructed on the fly, where the content type (e.g. page) is inserted into a template to form the string "edit own page content".

These strings are mostly used to call user_access, so to see where and how they're used, you may want to search for this function.