dependents array key not used in any place across the code

Sorry if this is a noisy issue.

While working on #898768: D7: drush dis [module] can disable profile I've found that the "files" array returned by `system_rebuild_module_data()` provide 'dependents' along with 'dependencies' (that is just the array in the .info file).
It also provides `requires` and `required_by` that are respectively the dependencies array parsed and the reverse dependencies (or dependents), calculated by drupal. Consider this object for the color module in a site installed with standard profile:

stdClass Object
(
    [uri] => modules/color/color.module
    [filename] => modules/color/color.module
    [name] => color
    [info] => Array
        (
            [name] => Color
            [description] => Allows administrators to change the color scheme of compatible themes.
            [package] => Core
            [version] => 7.0-dev
            [core] => 7.x
            [files] => Array
                (
                    [0] => color.module
                    [1] => color.install
                    [2] => color.test
                )
            [dependencies] => Array
                (
                )
            [dependents] => Array
                (
                )
            [php] => 5.2.0
            [bootstrap] => 0
        )
    [type] => module
    [status] => 1
    [schema_version] => 0
    [weight] => 0
    [required_by] => Array
        (
            [standard] => Array
                (
                    [name] => color
                )
        )
    [requires] => Array
        (
        )
    [sort] => -1
)

dependents and required_by doesn't match. I've digged into the code to see where is this coming from... with a simple grep I see that dependents is not used in any place. It's just an initialized key that is never used.

$ rgrep dependents includes/* modules/*
includes/module.inc: * @param $disable_dependents
includes/module.inc:function module_disable($module_list, $disable_dependents = TRUE) {
includes/module.inc:  if ($disable_dependents) {
includes/module.inc:    // Get all module data so we can find dependents and sort.
includes/update.inc:      'dependents' => array(),
modules/system/system.module:    'dependents' => array(),
modules/system/system.install:        'description' => "A serialized array containing information from the module's .info file; keys can include name, description, package, version, core, dependencies, dependents, and php.",
modules/system/system.install:    'description' => "A serialized array containing information from the module's .info file; keys can include name, description, package, version, core, dependencies, dependents, and php.",
modules/system/system.admin.inc:    // Mark dependents disabled so the user cannot remove required modules.
modules/system/system.admin.inc:    $dependents = array();

It is said in a description that dependents is a valid key for .info files but I don't see any usage for that. It's also not explained in "Writing .info files (Drupal 7.x)" -> http://drupal.org/node/542202 so if it's not something to drop from the code is something to add to the handbook :)

Please enlighten me. I can provide a patch to remove it from code or can improve the handbook.