Scott,
as far as I know, if one uses the samples of other music, he needs to carefuly consider licensing.
BUT!
If one creates the music on his own (without using any other samples), everything is OK even if creates his samples which reproduces any well-known melody. Any melody does not have any license, only author copyrights, if any.
Am I right here or I am wrong? Not sure.
I believe this varies in legislation by country. I've studied United States copyright law a lot, and in the US reproducing a known melody, even with your own instrument sounds, isn't legal. I'm not a lawyer, but I understand it to fall under what is called a "derivitave work," which is a copyright violation in the States.
I don't know what the law says in other nations, and I actually haven't listened to the music samples to compare yet, but in the US such similarities can lead to ugly legal battles if something doesn't sound original.
It could also happen to just be a coincidence, although that might be difficult to prove in court.
I will say that I like most of the soundtracks I've heard in the game so far, I'd hate to see any of them torn out.
If they sound too much the same, perhaps the author could make some changes to the melody?