Ok this question gets asked a lot. Here's the basic answer:
Those networks transmit those signals themselves which is in part paid for by commercials. It costs a lot of $$$ to do that. They will NOT let anyone else retransmit their content without paying for it.
Here is the problem. The networks provide the content for
free (with support from local commercials). There is nothing stopping them from providing that same feed to Apple, Roku or Google Chrome for
free as well, and allowing those providers to retransmit on their dime, not the network's. Cable companies will not provide their lines, service, etc for free since they are carrying the cost of the infrastructure to get said signal to you. Apple, Roku or Google
could charge you if they wanted (or not) and in this scenario, they are no different than Time Warner, Verizon, Comcast, Cox, etc... They have just become an alternative delivery method from the cable companies. Commercial rates could be adjusted to cover the expenses in providing the digital signal to these new providers.
ATv already has the pipeline, using the cable line / DSL line you already pay for, so this is really an issue of whether or not your local station should be able to charge you for the same signal that is otherwise free based on how you, the end user, receive it.