Schlesinger said, "For his fans, who still number in the millions, John Lennon's music is ageless. Even though he would be turning 70 today, had he lived."
Rolling Stone magazine's Anthony DeCurtis told CBS News, "These anniversaries provide an opportunity to reencounter Lennon. I mean, he was a very complicated figure."
Lennon evolved as a musician, and as a man before the eyes of the world.
DeCurtis has written the liner notes for two new box sets released to commemorate Lennon's birthday.
DeCurtis said, "You have the John Lennon writing a song like 'Come Together,' at the same time, you have somebody who can write a song like, you know, 'Jealous Guy.' 'I was feeling insecure. You might not love me anymore.'"
Schlesinger pointed out it's rare when a pop singer reveals himself as that multi-dimensional -- and rarer when the public gets to ride along as he ages and changes and morphs.
Michael Epstein, a filmmaker who has just completed a documentary on Lennon's life in New York City for the PBS series "American Masters," says of Lennon, "He was an astonishingly honest songwriter and poet and maybe one of the first truly honest rock 'n' rollers."
The documentary covers Lennon's music and his politics, as Lennon became an anti-war activist. It is up close and personal.
Schlesinger said the fact that films are still being made about John Lennon 30 years after his death says something about his legacy.
Epstein said, "I really miss that voice. That's -- I don't know what that voice would be saying right now, but I know it would be interesting. I don't know what that music would be right now, but, boy, he'd always be pushing himself and pushing others."
It begs the question, what would he be like today and what would he be doing?
DeCurtis said, "I do think there would have been a Beatles reunion. You know, I think enough time would have gone by and everybody would have tried it, and I think it would have been successful."
DeCurtis sees Lennon's legacy in many artists today -- even while Lennon purists might gag -- Lady Gaga.
DeCurtis explained, "The daringness and willingness to push boundaries, I think Lennon would have gotten a kick out of her."
Lennon's widow certainly got a kick out of her. Yoko Ono performed with her last week to commemorate Lennon's 70th.
But why does Lennon matter?
Epstein said, "Some of those songs really touched people. And some of those songs still matter in people's lives. Art has power beyond its moment. You know, great art has universality that is not stuck in its time."
On "The Early Show on Saturday Morning," co-anchor Chris Wragge added, "It is really amazing to believe he would have been 70 right now. Time does fly, but the songs, you could listen to them over and over."
Co-anchor Rebecca Jarvis said, "And they withstand the test of time so many generations. Kids today, you ask them who John Lennon is, and they will probably tell you who he is. They'll know."
Wragge said, "Everybody knows."