This is after effect to something like that happened coincidently, A single streamer who happens that his Avg count of viewers between 30k to 40k per day changed minds of many of viewers. Blizzard only promoting HotS through streamers their viewers already playing HotS and they don't need advertisment, they only there to see their favorite streamer playing skillfully. There is a huge difference between these and a streamer and his viewers who completely new to HotS and they experience it for the first time. This is the type of viewers/gamers you should target them.