On Wall Street “no one really talks about the broadcast side anymore — which tells you something, doesn’t it?” said Garth Ancier, who was a co-founder of the Fox network and who had stints running NBC and the WB, now defunct. The dominant emotion among his former colleagues, he said, is “tremendous frustration about working in a declining marketplace.”

The CBS network is in some ways the exception to the rules, and a possible blueprint for its rivals. It is by far the highest-rated network, and this season it lost only 3 percent of its audience between the ages of 18 and 49. Last week the CBS chief executive, Leslie Moonves, predicted that the network would once again persuade advertisers to pay roughly 10 percent more for commercial time than they did this time last year. The reason, he said, was simple: “We pull together mass audiences like no one else can.”

To skeptics, CBS is merely winning a game of musical chairs that will end with no chairs left. Studio heads and series creators privately complain that the broadcasters have largely stuck with the same arcane production strategy they have employed for decades: commissioning dozens of pilots early in the year, rushing them to completion and then holding a bake-off that rarely results in new hits. Some predict that the networks will eventually start cutting back on the number of hours a week they program with new shows.

But there is a trend toward trying more shows and running fewer repeats, reflecting the fact that the production business “is actually pretty healthy,” as Ms. Reif Cohen put it. Broadcast networks increasingly act as big billboards for new dramas and comedies, which are then sold and resold at a big profit to smaller channels, online services like Netflix and international channels. Networks are becoming “the first window of a bigger opportunity,” said David Bank, an analyst for RBC Capital Markets, who cautioned that “change is slower than it sometimes appears.”

The newest threat comes from Aereo, a service with an antenna array that scoops up the free signals of stations and then streams them over the Internet to paying subscribers, a tactic that the broadcasters say is illegal. Courts in New York have supported Aereo, spurring the start-up to expand to other markets — and to file a pre-emptive lawsuit against CBS, which has said it will sue in other courts.

The real risk for the broadcasters comes if cable and satellite distributors use Aereo’s tactic to circumvent laws that require them to pay stations for their signals. Then the subscriber fees that have propped up stations and their owners might evaporate. That is why CBS, Fox and Univision have threatened to take their signals off the air if Aereo continues to be upheld by the courts. Senator John McCain introduced a bill last week that would, among other measures, penalize the broadcasters if they were to do so.

Viewers, for their part, already penalize the networks often — for disappointing them, for changing shows’ time slots and for canceling shows prematurely. If this season is any indicator for next year, the networks will wind up canceling almost all of the shows they announce this week.