Watching Madonna at the Grammys on Sunday, I found myself feeling inexplicably sad. It was nothing she was doing. Onstage she looked like she was having the time of her life.

Cards on the table, I'm a fan. I would normally be the last person to criticize her. But the truth is her new song “Living for Love” really isn't one of her greatest. It's not even particularly memorable. But there she was still commanding the Grammy stage like it was 1984 and she was singing “Like a Virgin” and preparing to conquer the world all over again.

So I don't know what finally made led me to my double take, but I found myself having one. For the first time I started to wonder about her. She's been doing this for 30 years.

Kick, drop, roll, boogie. Doesn't it ever get old? And behind that, doesn't she?

In 1984 Madonna didn't preface her appearance with psychobabble self-help quotes about being true to yourself and telling everyone else to take a hike. She just rolled around in a wedding dress singing about sex. At the time that was already transgressive enough for most people.

But here she was again on Sunday night in 2015, still preternaturally youthful, her body worked out to within an inch of her life, and only her one or two faltering old lady steps in high heels to remind us that she's 56 if she's a day.

Critically it was a triumph. The papers were full of praise about her big moment. What she wore, how she danced, how young she looked.

No one really mentioned the song. No need. There was a time when she used to inspire people to dance. These days she seems to make people hope they'll keep their figure. That's a remarkable transition.

For a culture saturated in guns and school shooting mayhem, America likes to think it will live forever. No one is more emblematic of the refusal to keel over and die now than Madonna.

Millennial singers like Taylor Swift and Katy Perry claim to love her, but secretly they must be terrified her relentless three decade reign over pop culture, which shows no sign of ever coming to a close. I mean, how do you even follow that?

Onstage she was surrounded by dancing minotaurs, which middle America misidentified as stand-ins for Satan. The minotaurs apparently represented all the disappointing men she had loved and lost. It didn't matter that they turned out to be lousy, she had herself and her hope for tomorrow the song said.

“I'm not going to stop,” she sang. She looked like she meant it.

So it seems that even the biggest star in the world has to hope tomorrow will be better than today, then. That made her a little more human … until the lights, camera and the age defying choreography and sculpted hair started saying something else.

Still, for the first time ever I found myself wondering what she really gets from it. I used to think I knew, but now the point of it eludes me. At 56 wouldn't you rather have found love than still be in relentless pursuit of it? Wouldn't actual love be preferable to the fickle adulation of an audience? At what point would you cash your chips?

The company she's keeping onstage is getting younger and blander with each passing year, which helps explain some of her lingering relevance. Madonna is many things, but she is never dull. The 1950s era, nondescript stable of music stars that are now in the ascendant really can't challenge her, but that's not much of a comment on her career or her continuing relevance.

Meanwhile, Beyoncé appeared onstage with the inevitability of spring flowers. She thanked God for the award she was given. She thanks God every year.

She'll probably be thanking God in 2040. God apparently likes Beyoncé much more than He likes the rest of us.

Watching two top performers on Sunday, I was reminded that whatever appetite drove them toward stardom in the first place seems to be an appetite that is never appeased. It's the country's appetite, it's the world's – for love, youthfulness, adoration and applause.

It's never satiated, apparently. Not even after 30 years at the top. Isn't that a bit sad?