Bob Dylan has been worse than most at this, ripping of people's very personal versions of songs without any particular acknowledement. But, at the risk of being elitist, he is Bob Dylan. Shakespeare "borrowed" a lot too. and he was Shakespeare. behaviour which would be considered a bit twattish by us lesser mortals is I think permissible in serious geniuses. Look at the famous version of the House of the Rising Sun. Dylan stole the arrangement, the Animals stole it again from him. Who remembers who started it? I've even forgotten myself: dave van Ronk I think(but it could have been rick von Schmidt).