But networks are definitely on the decline. Case in point: “The Jay Leno Show” vs. “The Tonight Show with Conan O’Brien.” In the end, NBC has been shedding viewers, and no change of hosts or programs may bring them back. It’s not as though those viewers were sticking around for drama at 10 p.m. on other networks. Most likely they were turning to cable programs or on-demand offerings, TiVo, Hulu.com or the Internet.