For 20 years, Ted Harbert worked at ABC. He started there right out of college in 1977, when the network, along with CBS and NBC, was the only game in town and was the hit factory responsible for Happy Days; Charlie’s Angels; Rich Man, Poor Man; and Roots. By 1996, when Harbert was running ABC, those glory days were ending. All three networks were still colossal, but Fox had established its beachhead, and cable’s market penetration was almost complete. The '80s had seen the rise of MTV. And CNN was by then a big deal, not just an incinerator for Ted Turner’s extra cash. ESPN was competing aggressively. Individually, none of these channels got much of a rating most of the time, but the damage was starting to add up.

“People would say, ‘Oh, they’re nibbling away, they’re nibbling away,’ ” Harbert recalls. “And we would always say, ‘Well, they can nibble, but they’re never gonna really take us.’ And then they took us.”

Today, Harbert is president and C.E.O. of the Comcast Entertainment Group. He oversees The Style Network, G4—a six-year-old channel aimed at young men who love videogames—and C.E.G.’s most recognizable offering, E!, which features celebrity news. E! ranks 31st among the most-watched basic-cable channels, which means that, in general, less than 1 percent of America’s 112 million TV households are watching it during prime time. Yet Harbert is probably sleeping better these days than his former colleagues at the broadcast networks.

When Harbert talks about television, it’s with the sober clarity of someone who has looked at life from both sides now and has seen that only one business model is working. Cable networks target just those viewers who want what they have to offer. Broadcast networks want everyone. And the business of wanting everyone has never been worse. At the end of last season, ABC, CBS, and NBC reported their smallest combined audience ever, an event that has become a gloomy yearly occurrence. Meanwhile, cable—counting both basic channels and pay services like HBO and Showtime—now receives 55 percent of the total viewership.

It may be time to perform an autopsy on network TV, which some have pronounced officially dead at age 60, the victim of a lifetime of big spending, hard living, and bad planning. Here’s the coroner’s report: The evening newscasts have been mowed down by cable’s heat, spin, and round-the-clock immediacy. In prime time, nobody watches reruns anymore—and reruns, along with syndication, used to be the only way comedy and drama series, the heart of a network’s prime-time business, made money. (The way they make money now is...well, the networks will get back to you as soon as they figure that out.)

Speaking of old-school, half-hour sitcoms: Once, 50 of them were on the air at a time. Today, they’re all but gone. Suddenly, people just stopped liking them. Prime-time newsmagazines? Barely holding on. “Protected” time slots? Viewers accustomed to Web surfing and channel flipping at hyperspeed aren’t going to watch a new show just because they’re too lazy to change the channel after The Biggest Loser. The audience for daytime soaps, a profitable staple since TV’s infancy, has shrunk so dramatically that the form may vanish within a few years. This is all very bad news for a medium that hasn’t come up with a fresh format since 2000, when CBS launched the gold rush in reality-TV competitions with Survivor. (P.S.: Survivor isn’t what it used to be either.)

It’s unlikely that a broadcast network is ever again going to create a megahit like The Cosby Show, which at its mid-’80s peak drew as many as 50 million viewers an episode. For several years now, TV’s top event has been Fox’s American Idol. Last season, it drew 28.8 million viewers a week.

Conversations about the future of television tend to vault way past next week or next year into a world where schedules don’t exist and 10,000 programming options are all available at any moment, half of them fully inter­active. (Not enjoying this episode of Law & Order: Moonbase? That’s okay—you can change the plot!)