Home Guy:

Samsung and Nokia are simply responding to market demand. You can buy video cards for desktop computers that include TV tuners so that you can watch TV on your computer monitor, but those video cards don't sell well. For some reason, the 16 to 24 age group would much prefer to play video games and tweet on their desktop computers than watch TV.

The answer really lies in the fact that people are social animals. We prefer to be with other people given the option, whether it be to work or to play, we prefer the social interaction of "company". And, a computer that allows you to tweet with others and respond to tweets or to friend other people on facebook and respond to their facebook page is infinately more to our liking than the non-participatory one way conversation that happens on TV. There simply isn't a demand for TV on our computers because we're not as drawn to TV as we are to venues that allow social interaction like Twitter and Facebook.

PS:
This is definitely OT, but much of the reason why apes, dolphins and people have disproportionately larger brains than other members of the animal kingdom is that apes, dolphins and people have a social interaction with others of our own species. If you're an alligator lying in wait at a watering hole for a gazelle to come within striking range, you don't need a big brain. If that gazelle comes close enough for you to get your jaws around it, that's your meal and the thought of sharing it with other aligators doesn't even cross your mind. But, if you're not a big strong alligator, you may have to rely on the help of others to hunt down that gazelle. Some of you might chase the gazelle toward a narrow passage way where others of you may be lying in wait with a net or spears. In that case, the gazelle doesn't just go to the hunter that killed it, but to all who participated in capturing and killing it. And, it's that much more sophisticated social interaction associated with working together to hunt prey, and then sharing the fruits of the hunt with all of the other hunters that's required apes, dolphins and humans to develop a larger brain. So, social interaction is hard wired into our brains, and the one way conversation that TV can provide simply doesn't interest us as much as two or multiple way conversations with other people.