For Keillor, the explanation is simple:
"Our audience is composed of people who are ill," he deadpans. "They're too weak to get up and turn the dial. It's an audience of shut-ins."
He is one of America's best-known humorists, and that makes Keillor very much the star of the show. One of his recent lines: "There are so many things in New York that you'll never ever see again and, unfortunately, one of those may be your video camera."
But Garrison Keillor does more than entertain his audience. Each week, he talks his listeners to an imaginary world, a small town call Lake Wobegon where folks are, well, strangely familiar, and often seem to hail from another time -- maybe a better time.
"The thing that you don't want in radio is detail," he explains. "But the secret of telling a story on radio is to leave all of these blanks. And people fill all of this in."
Do his audiences remember enough of the things in the past so that they correct him, for instance, on the name of the Lutheran pastor's wife?
"I've never gotten the name of the Lutheran pastor's wife wrong. Her name is Judy," Keillor replies. "But I have gotten other characters wives wrong. and I get letters instantly the next week. E-mail instantly saying, 'Why has he taken up with Marilyn? What happened to Cindy?'"
In short, A Prairie Home Companion is like family, a delightful retreat. It's the world according to Garrison Keillor.
Tom Keith has been making "sounds" with Keillor for 25 years. (Most requested sound effect: tires spinning in the snow.) He says, "As soon as Garrison says, 'It was a quiet week in Lake Wobegon,' you can feel the audience settle down. This is it. This is what they came for, and they're ready to be told a story."
Gary Keillor (he changed his name when he grew up) was born in Anoka, Minn., the third of six children.
What was he like as a kid? Is there any of that little boy still in him?
"I sincerely hope not," he says with a laugh. "I was a strange child. And I was sort of toad-like... or newt-like. I saw photographs of myself as a child...and I shuddered to see them."
He grew up, he says, in a family of quiet, dour, evangelical fundamentalists.
"I'm in a business that rewards charm," he observes, "but I bring to this business the manners of a suspicious, rural, fundamentalist."
A suspicious fundamentalist who was already an established writer at The New Yorker when he and some friends began the local radio show that came to be a national treasure.
"We need him," says historian and radio peronality Studs Terkel. "I think, years from now, when all the artifacts of the day are forgotten, someone was around who was able to continue a tradition, the great literary tradition in the best sense of the word of story telling."
There came a time when Keillor decided not to do the radio show anymore.
"I got tired. I got really tired," he recalls. "I worked really, really hard. And I had delusions of becoming a novelist. And I also had delusions of living in New York. And so I did. I enjoyed myself for about a year and a half, and I wrote a not-very-good novel. And it was time to get back to suffering again."
Today, home for Garrison Keillor is back in St. Paul, Minn., where he lives with his wife, Jenny, and their 3-year-old daughter, Maia. His son, Jason, from a previous marriage, lives nearby in Wisconsin.
And, at 58, Keillor is writing now more than ever.
When he's not writing his show, he's busy writing magazine articles, an advice column for the online magazine Salon.com, teaching a writing class at the University of Minnesota, and finishing a novel due out this fall.
Along the way, a cottage industry has grown around him, including a store in Minnesota's Mall of America devoted to his fictional hometown, a place that makes its creator a little nostalgic.
"I have this old address book," he says. "About a third of the people in my address book are dead, and Lake Wobegon is a sort of cemetery in which I keep alive all of these people. And I try to keep them vivid, and, ever so often, funny, with a taste for a good time, a good meatloaf, and a story."