Any mmo worth their salt will provide numerous class balancing fixes, additional instances/dungeons, raid encounters etc in their 1st year to 18 months. ToR for example provided just as many 'deep' patches, so did Rift, GW2 etc. Since vanilla WoW has settled down into 4 'major' patches every expac cycle. That isn't a huge amount by anyone's standards, so what additional content do u get for your money over a FTP title? None
We are arguing semantics here, my point being, Blizzard provided lots of content to warrant a sub.