When making software, specially games, those resources like graphics and sounds are something "freaky" that's out of range of the developers brain and feasibility. I mean...sound effects like cool beeps: Who in the world can make them? Almost nobody of us, I guess ;)
So: Is there any good legal ressource for this kind of content, which allow to use them in Apps? How do all those developers make those cool and nice apps with nice music, nice sound and nice graphic without getting sued right away? Where do they get their high-quality contents?