NEW YORK - NBC's decision to give Jay Leno a show each weeknight leaves CBS and ABC the only major broadcasters still in the business of making scripted dramas for the last hour of prime-time.

Viewing habits are changing, and the well-turned adult drama is one more genre that broadcasters no longer have uniquely to themselves.

Let's pause here for a moment of silence and remember the fall of 1994, when the three networks aired “ER,” “Chicago Hope,” “Law & Order,” “Homicide: Life on the Street,” “NYPD Blue” and “Northern Exposure” at 10 p.m.

So far this season, not one program that airs in that hour is among the 10 most popular prime-time shows, according to Nielsen Media Research. “CSI: Miami,” at No. 11, comes closest.

Meanwhile, six of Nielsen's top 10 shows air at 9 p.m., among them “Grey's Anatomy,” “CSI: Crime Scene Investigation,” “Desperate Housewives” and “The Mentalist.”

Is 9 the new 10?

Networks have frequently used the 9 p.m. hour to air popular shows in the hope that viewers will stick around to try something new at 10. It hasn't worked much lately, but a textbook example was ABC using “Desperate Housewives” to introduce “Grey's Anatomy” a few years back.

Struggling networks are now contending with an unanticipated problem for their 10 p.m. shows - the digital video recorder. Instead of trying something new at 10, more people are simply watching something they've taped earlier.

“The 10 o'clock hour is still a very good hour for the networks,” said David Poltrack, CBS' chief researcher. “It's just that some of the people are watching the 9 o'clock shows.”

One thing Leno might have going for him is that people may be less likely to tape live, topical comedy to possibly watch later than they would a scripted drama, said Tim Brooks, author of “The Complete Directory to Prime-time Network and Cable TV Shows.”

CBS remains bullish about the later hour, where it has “Without a Trace,” “Numb3rs” and the two “CSI” spinoffs on the schedule this year.

“I know you've heard (for) a couple of days that the model is broken,” said CBS Corp. chief executive Leslie Moonves at a media conference last week. “I'm here to tell you - the model ain't broken. The model works ... You can still make a lot of money in network television; we are making a lot of money in network television. We like 10 o'clock shows.”

ABC has had less success in the time slot this season; only “Brothers & Sisters” is making some noise. Fox, the CW and My Network TV leave that hour to their local affiliates.

Over the past 15 years, average viewership at 10 p.m. on ABC, CBS and NBC has dropped by 44 percent, according to Nielsen. But it's not particular to that hour; viewership for all of prime time is down 43 percent.

Trouble for some people is opportunity for others. Many cable networks consider 10 p.m. their prime-time, since it's a good hour for younger viewers, and Fox and the CW aren't competing. Of the year's 10 most popular original dramas on cable networks, seven air at that hour - not even including series like “Mad Men” or “Californication.”

Only in the past few years have networks like TNT, USA, FX and AMC begun making original dramas.

Viewers have more choice now, not less, said Michael Wright, head of programming for TNT, TBS and Turner Classic Movies. Young viewers don't distinguish between broadcast and cable, he said.

“We are keenly aware that there are still people who are discovering original dramas on cable,” Wright said. “There's still a big upside for us.”