I think part of the problem is that some TV-based services, like VOD, must be piggybacked on an established game console (XBox 360) or DVR (TiVo) in order to succeed. Right now, VOD isn’t well developed enough, and doesn’t have the consumer demand to justify a dedicated box in the living room. (Perhaps the Roku Netflix box is an exception).
This situation is similar in the mobile world, where a handheld device generally can’t succeed unless it functionality set is anchored by phone, music or gaming functionality.