there was 8 million subs before BC came out. 11 by end of BC. Flying didn't bring in millions of millions and saying they did for Wrath at its peak of 12.5 when the last bad guy was the lich king, aka the villain everyone from the days of warcraft 3 knew and came to kill would get you laughed out of any argument.
Edited for correction and source.
http://www.powerwordgold.net/2013/07...2005-2013.html
- - - Updated - - -
You also can't make the argument that flying bought in 3 million players for BC either btw because again, BC central focus was going to outland and dealing with Kaelthas, Vashj, Illidan and Kil'Jaeden. Aka 4 of the main players in the Frozen throne expansion plus one of the major Areas for that expansion as well. People give more of a fuck about characters and locations than flying mounts.