Again, I would say good timing. They tapped in on teh fact that people like watching gameplay videos and they built a great system that made it easy for people

Again, I would say good timing. They tapped in on teh fact that people like watching gameplay videos and they built a great system that made it easy for people to use what were becoming affordable video capture frontends to publish live streams. And its a niche, but it's in a sense, a way more accessible niche than watching a random person lifecast. You're watching someone game. Which isn't that different from watching people play sports on TV.