Specialization is better than generalization for everyone but those who become hegemonic. If I come to Justin.tv I think "I don't know what I might find here (short of looking for pirated content)" and on Twitch I know "I'm going to see League of Legends".

It would be a bigger win to be the "Youtube of live streaming" but a harder win. Twitch ended up with a MASSIVE specialized win in online gaming, and they went with what was working.