> Customers buying .de domains have to be, necessarily, German
According to DENIC's TOS, the domain owner doesn't have to be German (as long as they appoint a Germany-based representative for receiving correspondence official and court correspondence, but that's not easyDNS' concern).
The product sold by EasyDNS is not targeted at the german market, it's targeted at people who (often, not always¹) want to offer their products (or information, or something else) to Germans.
¹ some just want some domain hack that ends in "de". I have a .es domain, despite having no intention of targeting the Spanish market, just because the name of the site ended in "es".
According to DENIC's TOS, the domain owner doesn't have to be German (as long as they appoint a Germany-based representative for receiving correspondence official and court correspondence, but that's not easyDNS' concern).