We have had an Apple TV since the first one came out and recently picked up a Roku 3 unit as well. We regularly watch Netflix and rent movies on the Apple TV and contrasting the Roku will be interesting. The Apple TV has a more limited set of apps than the Roku but we’ve been completely satisfied with it so far. The Roku has substantially more “channels” which are conduits to free and paid streaming content. Just in a few hours of exploration the Roku has demonstrated the astounding amount of entertainment (video/audio) available around the world in a variety of languages. The availability of local (even to the neighborhood level) as well as special and very specific interest content is also amazing. However, a drawback of the ease of creating and distributing this material is that much of it has fallen out of interest and has not been updated. You may find something that you like and subscribe to but it can quickly disappear or be updated at irregular and unpredictable intervals. This is in contrast to the episodic TV example of weekly or even daily shows.
The price of both devices ($100) are the same and it is easy to imagine a household where each TV/monitor has an attached streaming device.
We have also had Tivos since the first model as well and they have allowed time shifting (record for later playback) of broadcast and over the air TV programs (with the attached cable bill). Streaming provides the opportunity for free or low cost rental of content which for some people could easily take the place of broadcast episodic television programs. Having sufficient Internet bandwidth to your house (or more specifically to you) is your only requirement.
One thing is certain, I can’t imagine investing in movie theaters or broadcast TV of any kind. Streaming whenever, wherever and to whatever device you have available will only continue to increase and broadcast will follow the path of print media such as newspapers.