Of course they don't, it's not their job to police someone else's copyrights. Do you think Escape's shareholders wouldn't sue the officers of the company for breach of fiduciary duty if they discovered they were spending company funds to prop up some other business? If you own a copyright, it's your own job to enforce it. Why should copyright holders get to freeload off Grooveshark's work?
Of course they don't, it's not their job to police someone else's copyrights. Do you think Escape's shareholders wouldn't sue the officers of the company for breach of fiduciary duty if they discovered they were spending company funds to prop up some other business? If you own a copyright, it's your own job to enforce it. Why should copyright holders get to freeload off Grooveshark's work?