NBC's "Friends" has unexpectedly become TV's most popular show of the fall season, averaging 28.4 million viewers through five weeks, despite strong competition from CBS's "Survivor: Africa" for two of them. The plotlines may have helped: Rachel (Jennifer Aniston) is pregnant and Ross (David Schwimmer) is the dad. Thursday night, Sean Penn did a guest spot. Later this month, Brad Pitt, reportedly wearing a fat suit, is expected to make an appearance (his wife, Aniston, is on the show, in case you've been living in a cave). Remarking on the surprisingly high numbers, the sitcom's co-creator, David Crane, told the Associated Press: "Nobody expects that in the eighth year of a series. It's phenomenal." Many suggest "Friends" is doing well because viewers crave the familiar in a time of stress, which is like subscribing to the comfort-food theory. Crane believes that shortchanges the producers, writers and actors. "We have something to do with it," he said. "We're not just cozy." Last spring, when "Survivor" beat a lackluster set of "Friends" episodes regularly in the ratings there were real questions about a comeback. "It kind of felt like the series was done -- it had said what it had to say, it was good while it lasted but it was time to fold it up," said Robert Thompson, director of the Center for the Study of Popular Television at Syracuse University. Introducing two plot devices -- marriage and pregnancy -- is perceived as signs of creative desperation, he added. Instead, viewers who have figuratively "hung out" with the six main characters in their carefree youth have chosen to watch them grow up.