The point they are making is that most of America is turned off by classical and baroque music. Whether or not most children encountered it in school is less relevant than the fact that most children don't like it. I think the same could be said about the average American. I don't think the people who browse hacker news are the average American.
My theory is that classical music is so much complex so you literally have to level up your musical listening skills to make any sense of it.
Also they dynamics is different, typically a piece is building up some sort of context that adds to the experience - even more so than modern music - if you get home and someone blasts the final parts of a symphony on the stereo, it's easily perceived as just a cacophony of irritating tunes. It might have been enjoyable if you had been listening from the beginning.
It seems to me that a lot of recent songs reduce complexity even further - It seems common now with songs that are basically just a repeating theme with minor variations. I'm not saying it's bad, but it doesn't really require much effort to understand the structure, and it probably makes classical music seem even more alien.
