I also thought this was for Apple TV. Even though it isn't, it's theoretically possible to write apps that you control through your Apple TV by taking over one of the existing apps that you don't use. MLB is one of a few good candidates. Many of Apple TV's "apps" are actually javascript apps, though unfortunately they aren't just running a WebView.

When you load the MLB app, it requests javascript and assets from mlb.com and operates on some sort of XML document rather than an HTML DOM. At my office we use 3rd-gen Apple TVs for AirPlay presentations, and I did some experiments with making a custom app that showed a rotating list of clients. We used a Raspberry Pi that functioned as both webserver and DNS, then pointed the Apple TVs' DNS at the Pi to reroute all requests going to mlb.com.