If you think music repeats itself and that some songs sound exactly the freaking same, there could be a reason for that (well, other than piss poor artists being gobbled up by the machine): there's a finite limitation on how different songs can be. There is? Yep, says MATH.
The thinking is that there are a finite number of tones our ears can distinguished and a few notes in common in different songs can make the song sound similar. So will we ever reach a point where every melody has been recorded already? Watch the video and let math figure it out for you. [YouTube]