The short explanation is that Drupal uses a lot of numeric deltas in the block system; blocks are identified by the 'module' and the 'delta'. In early Drupal, delta was numeric, but somewhere along the line it was changed to be possibly a string. In modern Drupal, block overrides are easily done via block-MODULE-DELTA.tpl.php. The primary motivation to switch to string IDs everywhere is to make these deltas friendlier to themers:
block-user-0.tpl.php --> block-user-navigation.tpl.php
block-user-1.tpl.php --> block-user-login.tpl.php
You get the picture.
- always include CVS Id tags in all files
- add a new line after the CVS Id, if more code or phpdoc follows in the same code block
- fix bogus Id tags previously added