At last I found the information about how to, programmatically, define the default download to be shown @ http://sourceforge.net/projects/moodle/

Reference: http://sourceforge.net/p/forge/community-docs/Using%20the%20Release%20API/

Right now it always points to the last uploaded file. By using that API we can handle it without problems.

Surely, something implementable when we automate the index.php page and have the current (last) stable branch defined (MDLSITE-2053).

Note: Look to the comment, because it's also possible to change the human-readable format of all files. Consider doing it not only for the default one, but all them.

Ciao