Plagiarism
The thing here is it would have to be a melodic rip off... for example, if he was singing the same melody... it's sort of the same reason you can't copyright drum beats. The piano and chord structure is almost the same...true, at that one spot, but you would be surprised (or not so) about how many songs this happens to. However...the main issues are with direct melodic "rip-offs"... like what happened with Satriani. His issue was not with the chord structure, but with the melody... as that's the only thing he could have issue with legally. (visit SOCAN or ASCAP for copyright info)
I used to rule the world
Seas would rise when I gave the word
Now in the morning I sleep alone
Sweep the streets I used to own
This part of the Coldplay song Viva la Vida shared the same melody line as his guitar solo in "If I could fly".
Go find the full version. The melodic line is at :50 seconds in. This is the line that led to the law suit.
That was his issue. (not the chord structure)
But as for chord patterns in various songs running into each other... maybe watch this video for some fun clarity on the matter :)
Go to Axis of Awesome in youtube and look for 4 chord pop song
Shows the 4 same chords make up many many pop songs. I think they play about 40.