Steve Jobs, spe thinks TV is a hard go-to-market strategy since they give everyone a heavily subsidized set-top box, which makes it hard to sell them another one -- ask Apple TV, ask Roku, as Google in a few months.
Adding boxes and UIs doesn't work. To change that you need to go back to square one, tear up the box, and redesign it with a consistent UI across functions, and get it to consumer in a way they'll pay for. No way to do that yet.
Apple chose to prioritize phone over TV, tablet over TV, but it didn't matter since they couldn't get TV to market. Not a problem with vision or technology, just going to market.
Also, cable companies are regional, and there's no global standard like GSM is for phones. It's vulcanized.