Actors Tina Fey and Alec Baldwin are joined onset by the cast of "30 Rock" as they cut the cake during the "30 Rock" 100th Episode Celebration at Silver Cup Studios in the Queens borough of New York City. - 

Stacey Vanek Smith: Sad news for fans of NBC's "30 Rock." Liz Lemon and Jack Donagey will have just one more season.

Marketplace's Mitchell Hartman explains.

Mitchell Hartman: A fictional comedy show about another fictional comedy show, "30 Rock" stars Tina Fey as comedy writer Liz Lemon. Here she is getting into it with Alec Baldwin as the meddling network exec:

Tina Fey: Creativity to me is just like, pfft, like a bird, like a friendly bird, that embraces all ideas. Just like shoots out of its eyes all kinds of beauty.

Alec Baldwin: Wow, Lemon, this is like watching Hemingway write. Mark Hemingway.

Phillip Swann: The average person has no idea what's going on on that show.

That's Phillip Swann of TVPredictions.com.

Swann: And as a result they don't tune in. So the ratings have always been bad.

NBC is now ranked fourth among the major TV networks, and it's a while since it dominated comedy with shows like "Seinfeld."

Swann: Basically what NBC has to do is they have to take the reality stuff they have done well in terms of ratings and supplement that with some better dramas.

Those new dramas on NBC include a Jeckyll-and-Hyde doctor drama about a twisted neurosurgeon and a mystery set among the top 1 percent -- rich girl goes undercover as a maid in the house where she grew up, to catch a killer.

Must See TV? We'll see.

I'm Mitchell Hartman for Marketplace.

Follow Mitchell Hartman at @entrepreneurguy