This statement does not serve a purpose anymore.
In a long forgotten world it indicated the main version number of PHP which the code in the file was compatible to.
http://pear.php.net/manual/en/standards.sample.php
But since PHP 5.1 and later this is only marginally true.
Thus I propose to remove it from CakePHP.
Removing Router::defaults() as its not needed anymore.
Removing default routes from inside router.
Removing properties related to default routes.
Removing dead tests and updating tests.