Other then the principle of it I don't see why HBO cares that much about leaks. Unlike, network they don't rely on advertising revenue based on ratings. As far as I can tell if anything leaking the episodes early has only increased viewership rather then decreased it. Lastly, Game of Throne is already the most pirated show on the planet. The number of people watching the show early and the number of people stealing the show after it airs very likely has a huge overlap so the leaks themselves are not having a impact on the number of live viewers at all?