I have wondered this, too. Especially with the "traditional" patterns. How does someone say something is "theirs" when anyone can just make it?
I am making a quilt right now using a tattoo for inspiration, but the tattoo is sort of ripped off from a logo. By the time I have the applique worked out it's not exactly the same, but still similar. (I am not selling it or anything, but am a little nervous about putting the picture on my blog. I don't want to get in trouble.)