I haven't had a gold spammer whisper me in about 2 weeks now and only 4 pieces of mail in that time. Trust me. It''s better than a lot of MMOs out there (try playing **** and you'll see the difference).
If it is to limit gold spammers it is not working.
Oh it's working. Trust me. If they didn't limit the Buddy Keys, the Gold Spammers would be 5x worse than they are now.City of Heroes wnt through sheer hell when they introduced trail accounts. They were basically full accounts. Zone chat spam, /tell spam and e-mail spam coming out everyone's collective ears. They eventually severally restricted what trail accounts could do to prevent them from being abused by the spammers.