Hi Damyon,
I had the exact same issue, although I used the proper procedure of moving my entire moodle folder to a backup location, unzipping the fresh moodle installation, copying over my mods/blocks/themes, and then attempting the re-install. I did this THREE times using a freshly downloaded zip each time (twice taken from the download link in my moodle install, once directly from the moodle downloads page), and each time the version did not upgrade. Furthermore, I just checked the files in the raw zip, and the version.php file says
$release = '2.4.2+ (Build: 20130315)'; // Human-friendly version name
So I downloaded the .tgz file - worked like a charm. Are you sure the zipped version is correct? Or is it possible the server has the prior zipped version cached?
Thanks! Kraig