I'm not speaking for the site administrators and the following is speculation on my part.
Michigun originally posted his work on GT and it was linked here. I guess no one saw the need to steal his work and store it here. I also don't believe there was a need to register on GT when the .pdf was first linked (I don't think it was an attachment then either).
Anyway, I did a quick Google search and found the direct link and have added that on the first page.
Thanks for the heads up.
Regards,
Greg