Sometimes less is more. We already have a lot of interfaces around us, so why add yet another? In this case it's an extremely simple mechanism of streaming audio/video to a TV. Having dealt with a number of disastrous (but purportedly very flexible) oddball interfaces on every different device...no thanks.
Further there is a recurring mistake that people are making when they say that this can only play from the "web" (for instance http://daringfireball.net/linked/2013/07/25/chromecast-catch..., though he is hardly alone is saying something like that). The web is ubiquitous, and anything that can host a stream can become "the web". Expect file servers to add Chromecast sourcing in no time.
Further there is a recurring mistake that people are making when they say that this can only play from the "web" (for instance http://daringfireball.net/linked/2013/07/25/chromecast-catch..., though he is hardly alone is saying something like that). The web is ubiquitous, and anything that can host a stream can become "the web". Expect file servers to add Chromecast sourcing in no time.