Musicians rip each other off all the time. What shocks me is how open it is. In just a few minutes of brainstorming, I thought of 4 examples involving 8 songs.
These links will take you to the 30 second preview clips hosted on Amazon. Depending on your browser mood, you may have to scroll down and find the title of the relevant song in the tracklist and actually click on preview button or something. For each example, I suggest you listen to the preview clips in close succession. Some of these examples are more outrageous than others, but others are unabashed "homages" that the would artists admit, as in the case of David Bowie riffing off "Somewhere Over the Rainbow."
This is pretty astonishing. The stanzas are pretty much note-for-note identical. No one said that Madonna was the emblem of musical innovation, but still - she's ripping off Ozzy?