Not all of it - I watched Heroes Reborn last night on the NBC app, worked decently enough.
it's hit and miss. You are mostly screwed with free content to watch. That being said... especially with an iPhone/iPad... you do have plenty of options.
Most of the major networks offer streaming through their app/site without a cable sub on a limited basis. Depending on the network either the current week, or OLDER than the current week.
YouTube obviously.
Crackle offers a lot of content for free.
Yahoo screen offers quite a bit of free content.
Running around the net, there is plenty of free content.. Though yeah you have to look for it. Rick and Morty have new episodes for free for a week. Pokemon offers tons of episodes for free. Most cable channels offer a bunch of limited content for free.
Having a subscription to various services makes it really easy in that it gives you a ton of content all in one central (or many more centralized) places. Not having a sub, there is plenty of free content, but you have to look around for it.