With DigiXmas, you can submit your site to hundreds of directory in a semi-automated fashion. It is semi-automated because you must enter CAPTCHA where required, and must select the appropriate category for your link. Other than that, your site is submitted -- and if there's a human editor involved, then much headache is now created. Do you believe that spam can be thwarted by turning registration on in the link directory?
Yes. Some spam could be avoided that way. But real submitters might also run away. I only register on high quality directories. If I see the kind of the directory that there are hundreds of everywhere, no PR, no indexation, nothing, and it asks for registration, I just skip that one for good. For example, Vilesilencer recently created a special niche for directories that require registration, effectively moving them from the main list to the side-list.