Indeed, HBO's plans for direct subscribers[1] may be part of their strategy to be less dependent on the cable providers. When contracts expire and are up for renegotiation, HBO will have more leverage with Time Warner, Comcast. I think channels such as ESPN and HBO already do have quite a bit of leverage with cable providers but having their own direct link to consumers would give them even more.
To relate back to amazon, I'm guessing Jeff Bezos has to buy old HBO content at a loss to fill out the selections for Amazon Prime Video. That way, the $99 membership fee looks like a good value. Could amazon put a price squeeze on HBO? It doesn't look like it. Amazon needs HBO content more than HBO needs Amazon.
20 years ago, HBO didn't have these type of business options. If HBO didn't like Comcast terms, it would be unrealistic for HBO to start digging streets and laying new video cables to a million residential homes. With the internet, they don't have to. I'm not convinced that book publishers have no chess moves left to use.
[1]http://deadline.com/2014/10/richard-plepler-time-warner-inve...