The problem as it sits now with Roku, Apple TV, etc is that any of the tv apps for the various networks require you to already have a cable subscription to use them. I have two Apple TVs in my house. Mostly used for Netflix, Crackle, and streaming music, videos, etc from my iMac, iPad, iPhone, etc. (yeah, I'm an Apple guy)
In order to access any of the tv network channels, you have to sign into them with your existing cable subscription information. I can't use the HBO go app on any of my devices because we don't subscribe to HBO via our cable provider. I have been reading rumors for a while now that Apple at least has been in talks with the various networks to try to change this, but as it sits now, if you want cable channels thru any of these devices, you have to already subscribe to cable and get those particular channels. This of course kinda defeats the purpose in my mind, all I can watch via these apps are shows that have aired previously, and it's usually not all of their shows either. I may as well just watch them on regular tv.