Well, Aristophanes, if you would read into these cases closely (or just read the wikipedia page you provided), you will discover that there is no mention in a single one of these cases where the defendant lost on the basis of using another writer’s (I hesitate to even use the possessive in this case) chord progression.
So if the plaintiffs in these cases did not win on the basis of a copied chord progression, how did they win? They won based on an IP concept called “striking similarity”. My bet is that in nearly all of the cases (many of which I am quite familiar with), the court felt that either the melody or the lyric (or both) met the criterion of the “striking similarity” tests.
I want to make it clear that I am not defending the SS test. It is a rule that is both vague and arbitrary at the same time, designed to keep new artistic competition from ever entering the field without receiving multiple court summons’s. My only point is that what you said is untrue and legally universal. But, I will disclaimer that statement by saying that I am sure if one dug deep enough, one might be able to find a case where the chord progression charge held up in court at one point or another, however it would be a distinct exception, not the rule. While I don’t want to make an argument from authority, I do work in this business, and I studied it (including rigorous IP law classes) both in and out of the university classroom, and I have never heard of such a charge ever winning a case on it’s own, and I have had clients who have tried.