I am going to say what is on every Western gamer's mind, but they are afraid to say it because they don't want to upset their Japanophile friends:
No MMORPG from Japan will ever reach comparable numbers to the World of Warcraft. Why? Final Fantasy is too Japan-centric for those who have never heard of Final Fantasy, while anyone who has read a Lord of the Rings book or a Forgotten Realms or Dragonlance fantasy novel inspired by J.R.R. Tolkien can easily relate to Warcraft.
Final Fantasy 11 has been out since 2002 and according to Wikipedia (take it how you want to take it), "In April 2009, Square Enix announced that the total number of active characters exceeded 2 million for the first time in game history."
7 years to reach 2 million monthly subscribers, while when I played the World of Warcraft exclusively from January 2007 until July 2009, the lowest subscriber number I ran across was 6 million according to the WoW Census on www.warcraftrealms.com.
Redressing Final Fantasy 11 as Final Fantasy 14 is cute, but the past numbers speak for themselves and portend what is more than likely to come in the future.
I would call Final Fantasy 11 a failure in comparison to the World of Warcraft, but that is as trite as saying "its hot" during a sunny day.