Here is TJR's follow up analysis that gives his opinion:
So - my amateur opinion? I don't think that you can make a copyright claim on a chord progression. There are literally thousands of songs with virtually the same progressions but are clearly different songs. Taurus is an instrumental that goes a completely different direction after the opening riff, and Stairway to Heaven does the same. Did Page copy the gist of the progression? Maybe, but to me that is no plagiarism.