Er, I seem to recall that we DID look at that study here a year or two back, and that I was one of the very few (perhaps the only?) contributor to that thread who actually bothered to go and look at where the source material for the "million song database" had come from and how it was put together. I'll see if I can dig it out when I have the time but my memory of the thread is that the way they'd selected songs for inclusion in the database left a lot to be desired....the way they'd structured it was such that it was skewed...so if your sample's skewed, the results are likely to be too.

And I AM an old fart myself....just not one who's mind is still mired in "good ol' days", trying to be *objective* and filtering out the fact that my first instinct is just to recall the good stuff from "back then" while having edited out of my memory the sea of dross it floated in. And realising that today is very little different....some decent stuff plus a lot of manufactured clone-sound.

When I go back and look at the charts of the late 50s and early 60s, I just can't agree with either you or the "study"...the more popular stuff back then, with a very few notable exceptions, was generally very simple, 3 or 4 quite basic chords put together in very predictable ways. Contrast with even fairly simple more modern songs like Cooper Temple Clause's "Who Needs Enemies?" (10 chords, including several flattened "sus2"s and "13"s) and Arcade Fire's "Intervention" which lulls you with its initial Am, F, C and G, then throws in Em and E before adding Bs Ds and Bms towards the end....a very very simple song but the little shifts make it more interesting to listen to as it builds...much more than I can say for the basic repetitive nature of most stuff from the 50s and early 60s:
Intervention Live

I agree entirely about the over-compression. In fact, the trend among the newer generation of sound engineers (and I know half a dozen of them) has been to fight against this over the last 5-6 years....and at last they show signs of being listened to!