Our customer asked us for the web application demo on Sony TV. I quickly found that for Sony the situation is a bit different then on LG, Samsung or Panasonic and seems to be much worse. There is no Sony web SDK for TV developers - there was a platform called Applicast for Sony Bravia TV - but seems that it is already out-dated and released only for Japan. After searching the Internet I found that another approach is to use the Yahoo Connected TV widgets, but seems that development is limited to very few countries...
Finally I ended with the Sony Google TV and the tutorial here, which shows how to move the web application to the Google TV.
So my question is:
The development environment for Sony Google TV is the Android development environment which is of course quite mature and robust.
If you have a web application, the user can use the browser of course but you can also wrap the web application in an Android application ... Where the Android application just starts the browser at a particular URL, or uses a webview to load the web page as a "widget" within a larger layout that can include other non-web elements. I'm not sure what you mean by "is using the webview the only way ...". It's quite flexible. you can load web assets from the web or from assets bundled in the application. It's quite flexible. I'm not sure what else you could ask for.
I have no experience with streaming video on a Google TV, but here's a link that indicates that it is supported, and has recently been "enhanced",
http://www.engadget.com/2012/02/03/google-tv-3-2-update-enhances-hls-video-streaming-support-plex/