Let's be honest: Half of the time, the actors chosen for television shows are not well known yet. I say yet because the show will most likely be their claim to fame unless it bombs after two episodes. But it is the celebrities willing to guest star that gauges how popular a show is.
For instance, "Smash" has been dropping names like nobody's business lately, with guest stars such as Nick Jonas and Bernadette Peters in recent episodes. The majority of the cast is labeled with "and introducing" before actors' names when it comes to main characters. Katharine McPhee and Megan Hilty are not the big names. Debra Messing and Anjelica Huston flash in lights, but remain secondary characters.
The biggest measurement of the success of a show that features musical numbers is the guests, whether they're from Broadway, television, movies, or iTunes. "Glee" is another perfect example, with guest stars such as Ricky Martin, Idina Menzel, Josh Groban, Gwyneth Paltrow, John Stamos and Kristen Chenoweth. This show is so popular and off the charts that many stars want to get in on the mania before it dies down (like right about now). If celebrities want to make some extra bank, they know they better pony up and try to pop up on a show for increased viewers or millions of downloads.
Then there is the next level down in shows such as "Once Upon a Time."
They have a couple of somewhat known actresses, such as Ginnifer Goodwin and Jennifer Morrison from "House," and have only managed to snag one or two guests, like Emilie de Ravin from "Lost." It's about on the same level as "New Girl," with the known Zooey Deschanel and a sprinkling of Justin Long.
Face it: If a network wants a show to succeed, they're going to need at least one or two names that viewers have heard before. "Parks and Recreation" has Amy Poehler, and "True Blood" has Anna Paquin. Now, if you want to make some serious cash, throw in as many as possible, like "30 Rock."
