The break with the past in 1964 does seem more complete than subsequent big changes. The charts were suddenly full of inanely grinning beat combos. But I think that if you looked at the singles charts you'd never detect the other great upheavals such as punk, dance and hip hop. Maybe because in 64 everyone buying pop singles were of the same age but later there were enough mums and dads and older brothers and sisters buying records to keep the charts occupied by Shaking Sevens and Racey. rock had splintered and had so many different audiences that 1964 just couldn't happen again
That's interesting looking at the recent study on changes in popular music. This study looked at chord progressions, rhythms, sonic qualities etc. The study concluded that while the early sixties was a big change, the biggest revolution was the hip hop and rap era.
The thing is, according to the methodology, they took their sample from the U.S. Billboard Hot 100 charts. Now to me that only represents a windows on popular music. Beatles, stones, the who etc suddenly appearing on the charts all would have shown breaks and developments from the past but their antecedents would have been more obvious ( Holly to Beatles and Berry to Stones isn't that much of a stretch for instance musically) The change would have been more of one in degree rather than a fundamental shift.
Now if hip hop and rap start appearing on the charts in the 90s that's clearly going to look a bigger break musically with Flock of Seagulls and Duran Duran. But rap and hip hop themselves grew out of earlier musical styles. It's just that these didn't appear in the Top 100. The evolution wasn't so much in the music then in the shift in tastes which saw this style become a large seller. Rap had been around since at least the 70s
And punk etc would barely be a blip in the late 70 s as it didn't tend to figure much on the singles charts. And progressive rock, being an album based form, also wouldn't have been noticed at all.
The methodology seemed to throw up other curious results, such as what they claim was the disappearance of the dominant 7th chord from pop from the early 60s. The Beatles were big exponents of this chord. Perhaps only analysing 30 second snippets of top 100 songs, which is what they did, simply missed this type of thing.
Still. Interesting study.
http://time.com/3849844/music-hip-hop-revolution-pop-billboard-hot-100/Full study here for those with time
http://rsos.royalsocietypublishing.org/content/2/5/150081I should add that the authors acknowledge the limitations of their sample etc.