It is also good for the market to have two larger game channels (youtube and twitch, yes there are Everyplay, hitbox and there will be more now this deal happened).

Amazon is really hands-off with acquisitions for the most part such as Zappos and Audible. They primarily add to the offerings by cheaper fulfillment or server/bandwidth/cpu costs and more. I think they will treat twitch better than if it was just integrated into youtube.

Also, it shows a dedication to game developers and supporting marketing of games on their platforms and others. Amazon buying them is actually better for Twitch and the gaming/let's play type new marketing channels.