Our own Alex Ziebart, the darkness that dwells in the souls of all, went into heroic Sethekk today and confirmed it. As of right now, Anzu is simply there if you enter the instance on heroic. No need of a druid who has completed or is on the Vanquish the Raven God quest; just walk in and there he is. As of yet, there's no information on the intended nature of this change; it wasn't mentioned in the big mount availability changes post for 4.0.3. As soon as we find out, we'll let you know.
World of Warcraft: Cataclysm will destroy Azeroth as we know it; nothing will be the same! In WoW Insider's Guide to Cataclysm, you can find out everything you need to know about WoW's third expansion (available Dec. 7, 2010), from brand new races to revamped quests and zones. Visit our Cataclysm news category for the most recent posts having to do with the Cataclysm expansion.