Listen to the part I linked to. The “You are pettin’ and I’m a frettin’” and compare with the Led Zepplin “You need coolin’ and baby I’m not foolin’” part. Or even the beggining “You got yearnin’ and I’m a burnin’” part. Lyrically, rhythmically, and melodically, they’re quite similar. Then you have the “baby way down inside” part that echoes pretty clearly the Led Zeppelin “Way Down Inside” breakdown in “Whole Lotta Love.” And the chord progression the back, with the rocking back and forth between those blues notes is pretty clearly established in “Whole Lotta Love,” in my opinion. So, between the melodic similarities, the musical similarities, the lyrical similarities, yeah, I think Willie Dixon has a stronger claim here than “Taurus” vs “Stairway.” Now, there are substantial differences, too, of course. And I could maybe be persuaded to decide in Led Zeppelin’s favor. But to say there’s no musical similarity is ludicrous to me. These are more alike (to me) than “Taurus” and “Stairway”.
They’re the same damn song. Sure, LZ put their own spin on it and contributed their own musical ideas. So did the Doors when they recorded “Back Door Man”–they completely changed the melody and the chords, but they didn’t try to cheat Willie Dixon out of a full composer credit. When Cream did “Crossroads,” the results bore little resemblance to Robert Johnson’s original, but they still gave Johnson full credit. For Zeppelin, even after being sued, to cut Willie Dixon in for a lousy one-fifth of the credit for their take on his song is obscene.