Yes they are. They did it when they released The Burning Crusade expansion. They did it again when they released the Wrath of the Lich King expansion. And yet again with the Mists of Pandaria expansion. Any other questions?
(and fwiw I enjoyed Cataclysm more than WotLK as an expansion because I felt like cataclysm was a great expansion for raiding, so in my book it was also a good expansion but I leave it out because general consensus is that it was not).