Mark's Book Marks asks for the same information for a partner account.
See a lot of webmasters will cheat and then just come back with a different domain and email address once they get blacklisted.
Its a lot more trouble to get a new mailing address and phone number just to keep on cheating on your TGP galleries.
If you owned a site that had 1,000,000 plus bookmarkers you'd be careful who you linked to as well. And say what you like about bookmark traffic, but sublime's traffic does convert well. (As does Mark's BTW)
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Did somebody say Free Content?