"Those (three) don't have any fear," said Dylan's son Jakob, frontman of the Wallflowers. "It's not something you can learn in a music guidebook. Being fearless is just an instinct you have. And you have to trust your audience. People want to see artists task risks, they want to see them be flippant, they want to see them indulge themselves, they want to see them come back, they want to see the quality that was there. I think that's the relationship you have to have with an audience."

They create a mystique. Build a mystery, and fans want to unlock it. The young Dylan made up stories about his background. His interviews are few and far between, his pronouncements from the stage as enigmatic as they are rare. Even his 2002 memoir was as confounding as it was revealing.

Springsteen is clearly more extroverted, often telling tales of his life to introduce songs in concert or giving in-depth interviews to promote his albums. But he doesn't talk about his children and family, and he shares no personal information in his social-network postings.

While Madonna is the master of media manipulation, who really knows the real Madge? Her interviews are like performance art (see her appearances on "The Late Show With David Letterman."). She loves creating a mystery.

"The secret to longevity, as opposed to just being famous, is they've kept something back from their audience," said consultant Pollack. "I think sometimes today artists share too much with their audience. The great ones don't sit down and tell you what every lyric means, and they don't need to tell you they went to Starbucks at 3 p.m."

They've cultivated new audiences. Back in the late 1980s, Dylan picked up fresh followers by touring with the Grateful Dead. Even younger Deadheads are showing up at his concerts in this century. Madonna, too, has piqued the interest of young fans of Lady Gaga, Britney Spears and Beyonce who are curious to see the mother of them all. And of course, Gen Y-ers and millennials weaned on their parents' records are drawn to check out these legends.

They have good business sense. These veterans know about supply and demand. Dylan is fond of playing small, entertainment-starved towns, and he keeps his tickets priced modestly. By contrast, Springsteen and Madonna allow demand to build by touring only every three to five years, in conjunction with new albums.

They don't do greatest-hits shows. All three continue to make new recordings that, while not always classics or big sellers, are credible.

On Springsteen's current tour, he has been performing six to eight songs from his recent "Wrecking Ball" album. Madonna usually offers eight selections from 2012's slow-selling "MDNA." Then there's Dylan, ever the iconoclast, who did not play a single song from his widely acclaimed new album "Tempest" in his first 10 shows after it was released in September.

In concert, each icon has a different kind of impact on audiences — Madonna gives an erotic charge, Springsteen uplifts and Dylan provokes.

"These three artists are not coasting," DeCurtis said. "They're challenging themselves in some way, and that's exciting. That's what people go to see."