For for a long time TunerFreeMCE has been the best addin for bringing on demand TV into Windows Media Center with out the need for a TV Tuner (hence the name). Martin Millmore the developer of TunerFree has brought the app to the Windows Store, bringing TV to Windows 8 and Windows RT.
The app has content from BBC iPlayer, ITV, Channel 4, Five, Dave, Hulu, NASA TV and ABC Australia. You can browse the channels and search for TV Shows.
Because some of the channels (like BBC iPlayer) use Flash when you select a TV show it launches the web version of the page due to limitations of the SDK and the streaming sites.
I have been playing with and it works great on my Surface RT, you can browse the channels content and use the search charm to find shows. Once you select a show it opens the TV programme in the Metro version of Internet Explorer. I tested BBC, ITV, Channel 4 and Dave, they all played perfectly. Channel 5 seemed to be a hit and miss but it did work eventually. When you start the app for the first time you can pick which channels you want including in the app so you don’t have to have channels which aren’t available in your region showing up in the searches.
It’s a great app to use on the Surface and the app is completely free from the Windows Store.