Yes, you need cable to get WatchESPN, but once you've logged in you're effectively untethered from your TV.
100% disagree that ESPN hold's the key to the future of live sports.
It will be someone who now is on the periphery, without the baggage of multi-year contracts and relationships. Someone with the technical know-how and ingenuity to put the customer on the left side of the equation.
It won't happen, initially, with the bigger sports but as monthly dollars shift from cable to mobile devices, someone will be in prime position to introduce the right solution.