The most unexpected thing about the “American Idol” phenomenon is the notion of demographics. The media know-it-all (yours truly) has a silly idea that Fox’s talent show is a hit because millions of teenage girls (who clearly don’t know what’s good for them!) tune in each week and skew the Nielsen rating toward mindless pap.

But then you go to an “American Idols Live!” concert tour, like Sunday’s packed house at the FedExForum, and you see that it’s not just teenagers. It’s grandmothers riding those scooter things. It’s middle-aged guys, like me. It’s all kinds of people. People who really love music and who are also thinking critically about it.

In fact, the tour’s line-up gives you the sneaking suspicion that the American people actually know what they’re doing when they phone in their votes, and that, at least in this past season, they voted correctly.

The concert, featuring the top 10 winners, counts down in the order that the singers got booted from the competition, starting with beefy Michael Sarver (10), who should switch to country music, Megan Joy (9), whose voice is made for smooth jazz, and Scott MacIntyre (8), who should open a piano bar with his name on it.

In the middle are the singers whose careers could go either way given additional training and good management. Our Memphis girl, Lil Rounds (7), is among them. On the show, she was the risk-taker, picking songs by Celine Dion and Bette Midler among others. In concert, she settled on unsurprising though nicely rendered tunes by Mary J. Blige (“Be Without You” and “Just Fine”), Alicia Keys (“No One”) and Beyonce’s (“Single Ladies”).

Anoop Desai (6), Matt Giraud (5), Allison Iraheta (4), and Danny Gokey (3) each had one or two numbers that stuck out, but none, it seemed, with the interesting rearrangements that got them points for artistry on the television show.

As to the great national debate over who should have won “American Idol” this year — Adam Lambert or Kris Allen — the stadium tour settles it. I concede to the masses. Adam gets my props for glam-rocking the house with a David Bowie medley. He’s the best showman, for sure, in a Judas Priest-meets-Liberace studded leather jacket with tails. But at some point, his shrieking becomes self-indulgent and irritating. Adam Lambert is all about Adam Lambert.

The wholesome Arkansas boy, Kris Allen, playing guitar and piano, earnestly covering songs by The Killers, Bill Withers, Matchbox 20 and The Beatles, brought something for everyone, of every age. No wonder he won. He plays for the true “American Idol” demographic.