Mixed feelings on this one. It was only a matter of time before someone pointed out PiU's similarity to Subterranean Homesick Blues, so he took the best option and 'fessed up. See also Zeppelin, Cream, and decades' worth of folk & blues etc.
Having said that, I do think there are legitimate cases where more unique melodies have clearly been pinched.
But I'll let the legal eagles worry about all that.