Far as i know copyright law on music and recordings, once someone goes through the trouble to record a song and publish it, publish as in produce and sell a record to anyone person with their name on it with a copyright symbol it is theoretically copyrighted to them. However someone could come along to dispute this and if they have acutally shelled out money to pay for the copyrights to soem material that has been puiblished and sold they may have an easier time in court proving that they own it and have the rights to sell it.
As for making sure no one does what you do or plays what you play or if you are playing something that someone else already wrote just become musically aware in a few ways. If you play something that sounds cool remember your influences and which bands you have been listenting to lately, those usually influence how I write since it is music i like to listen to and play. I'm, sure the same is true for many people. The easiest way to get around this is just know which style you are shooting for and write something that sounds like if fits a specific genre. Otherwise be experimental and combine influences.
About this intellectual musical communism thing, that sounds like a bitchen idea, though theoretically anything can be good. Music theory is good for just about one thing engineering music. An on a count of technicallity it's probaly true that nothing you come up with in this day and age is original and new to the ears of people. The point here is to take what you know and make it into someting that sounds new, or is some variation that no one has ever heard. Look at the crap paparoach released some of it parrallels Iron maiden perfectly just cleare recording quality and a key change.