The reason an address is needed is for the WHOIS records of the domain, such as for the Abuse contact information of the domain and so that the domain can be verified as being owned to a particular person. A good example can found with x10Hosting's or Google's WHOIS records. I know there are services out there that can mask your WHOIS records for you, however I don't know if those violate any domain name terms of service for WHOIS fraud.