Except one problem. They are, or more precisely can by. If you only record same song with same music and same arrangement then you have only copyright of your recording. But when you change arrangement, or melody, or text or anything else you also have copyright for changed parts. Like Johnny Cash Hurt has completetly different arrangement than NIN. You of course still need to pay for copyright owner of original for usage of their part, but they can't simply take your version and sell as their.