There are two factors.

First, here's an analogous question: why do people still listen to the radio when you can download entire discographies at the click of a button? The answer is the trait that radio and podcasts share--the DJ.

A DJ is, for the purpose of this comment, someone sitting there on the other end of the line, sharing music with you and thinking carefully about what to play next to maximize your enjoyment, and sometimes offering commentary in-between. People like DJs. A DJ, on a station you like, is like a friend of yours--at minimum, immersed in the same culture as you, whether by physical proximity or by interest--who can tell you about all the new and great music they've been listening to, except that that's their whole job, so A: they're really very good at it, and B: you can ignore them sometimes when you don't like what they're saying without upsetting them. The station, in some ways, is the DJ.

Television stations are their programming. Even if the commentary isn't there (though wouldn't it be interesting if it was? a station with a live impressario, critically evaluating the progress of a show on the breaks while the advertisements rolled in a sidebar?), the playlist-y-ness is there, which is what's important. Playlistyness is what's making it hard to win the Netflix prize: there's something a DJ knows about their audience that lets them recommend certain otherwise-controversial choices, that the Netflix algorithms and the iTunes Genius and so on just can't manage. (In my opinion, it's likely the ability to take a real, human stance on a divisive piece of media that actually pushes the division in one direction or another, and that's something machines will never be able to do, at least until some time after they get suffrage.)

Now, the second factor: why do some people like Internet radio and not podcasts? Internet radio is live and source-ubiquitous. Live in that, like radio and television, things can happen on the stream as they happen in reality: there can be news reports, interviews, call-in shows, and so on. Clothes can malfunction. This feels real.

Some television shows are live, obviously. Beyond that, the programming choices usually don't feel live, but the ads do--whatever ads air are always part of a corporation's newest marketing strategy, which is, if they're doing their job, 100% pure current-and-targeted pop-culture. Thus, you can look at an advertisement (in any content-digest medium, such as a magazine) and immediately feel immersed in the culture and time which created it, which, if it's the present, makes it feel more "live." (Magazine ads, though, are designed to culture-decay more gracefully precisely because magazines lay about in places like waiting rooms for so long. You don't want to disturb people by immersing them in a foreign (or even just old) "live", so you back off on the feeling a bit.)

Source-ubiquity is just the concept that, when you turn on your TV and I turn on my TV, they have the same things available (unlike, say, your iPod and my iPod), and more importantly, we can find the same thing at the same time (assuming we live in the same timezone), regardless of our intention to do that. Couples can watch TV together over the telephone, without it occurring to them that they're doing so. The important part is that this doesn't require any special synchronization--you don't have to say "1, 2, 3, press play", or get a group over for football; you only have to turn on your sets and flip around a bit. Your friends (who you assumably share interests with) will anneal to the same channel as you, and then be fed the same program.

"Every household in America was listening to the president's inaugural address" is a powerful statement: everyone, sitting around in their houses, was in one virtual place at the same time. I can't imagine any event that would cause everyone on (or even a large chunk of) the Internet to go to the same site at the same time; the nearest we have here are Alternate Reality Games, where planned "events" (such as characters appearing in chatrooms, or websites being altered) happen as parts of a continuing story.

"The Evening News" is the purest form of source-ubiquity: the idea of "the News" is that there are a certain number of facts that you can rely on other people to be statistically likely to be aware of, because they are "news"; they are news because they were put into a source-ubiquitous medium at a time when a lot of people were watching. You watch the News to find out not what's important to your own life (if you've important news, someone you actally know will tell you soon enough), but what's important to the "live"--the current culture, weighted inversely proportionally to the square of time. (You can picture journalists riding a moving "live" hyperbola like a wave if you like.)

Now a digression, that I'll justify in a moment: pop culture in general, but celebrity culture in particular, are important, because they give people some way to relate to strangers who might be very foreign to them. Celebrity evolved out of our desire to continue to gossip about things as we moved out of farmland and into dense cities, where the stranger on the corner won't know your neighbours. They will know about which movie star had what rapper's baby, and so you talk about that--and so you read about that. Entertainment Tonight is, if you can imagine it, an existential battlefront in the war against meaninglessness in the face of population explosion.

"Live", together with source-ubiquity, encourage celebrity. You can talk to the stranger on the corner about what you saw "at seven last night," and they'll know what you mean. You can gossip about fictional characters as if they were real people, precisely because you know that everyone around you gets the same cable package.

Television is integral to our culture today. If we truly do abandon it, not individually but as a culture, we'll need to create something that works like it within our new, peer-to-peer reality, or we'll lose all these benefits. "Web communities" are a step towards source-ubiquity. Podcasts are playlist-y. And the main benefit of "Web 2.0" was, I think, to make most of the web feel "live." However, I think there are very few sites or applications, currently, that capture all three benefits the way television and radio do. That's definitely a market opportunity, though probably not just yet ;)

> Watching shows in just one room, wired to a wall

Those are legacy, though. Let's hope those go away in the redesign.