The orc leader is Lord Of Clans... Not Warchief. The Warchief since Thrall's Horde is the leader/Chief Commander of the whole organization, with all the races.
I replied to someone that i thought was saying that the Orc leaders title was "Warchief", i just made that point saying that is incorrect, but has he stated after i just misunderstood him.
About your point that the Orc leader title is "Lord of the Clans", well it is the title of a good book but the Orc tend to call their leaders Chieftens/Farseer, and letting the "Lord" for a position like a General (HighWar"lord" for example).
Even so, seeing Thrall the Lord of the Clans (or whatever will represent the Orc Race on the Horde) is very cool too!