What in the hell are you talking about? When has Blizzard ever stated that that they want to annualise WoW, and what has Blizzard ever done previously in WoW's history to make it seem like they want to release an expansion every year? Each 'stage' of WoW has lasted roughly 2 years.
'Vanilla': November 23, 2004
TBC: January 16, 2007 (Pretty close to, 2 years)
WoTLK: November 13, 2008 (Again near enough 2 years)
Cata: December 7, 2010 (What d'ya know 2 years)
I really have no idea what gave you that impression....