My comments below are based on US Copyright laws, which may be different in other countries.
You can copyright a material, but you can't copyright a script.
For that you have patients which btw, don't apply to lyrics, pictures and the like.
It's like saying that it's illegal for me to make a game that has experience/levels system because it was already done by DAoC and such.
Wrong. You can't copyright concepts. You can copyright a specific implementation of those concepts. It's like you can't get a patent on ice, but you can get a patent on a specific technology used to make ice.
I could write a song that's almost like nothing else matters but change a few words here and there and there you have it - a new song...
Also wrong. It's called a derivative work, and is protected under copyright law. Your "new" work has to be substantially different. Look at what happened to Vanilla Ice when he sampled the Queen base riff for "Ice, Ice Baby" a few years ago.
Ahhh heck, while we're at it, how about we make it illegal for kids to rip pictures out of their magazines and tack them to their walls, since I'm sure this is starting to hurt the revenue of the poster industry.
Wrong analogy. You paid for the magazine.
Yes musics copyright ends within 5 years of it's starting date or less depending on it's popularity etc.
For anyone that wants to read the basics of copyright, there is a very easy-to-read document published by the copyright office that speaks in plain language. You can also read the specific legal text. The plain language version is here
and their FAQ is here