You're right that it's okay to use the ideas in another person's quilt, but "copying" the quilt is not permissible.
See #6: "Copying a quilt would be an infringement, but because ideas are not copyight, it is acceptable to use another quilt for ideas."
You're right that I based my diamond log cabin star design on quilts that I saw elsewhere. I first saw the design on a site selling quilts, and later in a book of quilts from the 20th century. I also found references to building a log cabin around a diamond shape in other books and internet sites. It was okay to copy this design, because the block is clearly in the public domain, and my quilt design was not a total copy of any other. It was in researching my right to make this quilt (since I couldn't find a pattern anywhere) that I came across the reference I cited.
Judy's quilt is another story. The quilt design is clearly copyrighted in her book. Using the quilt design for ideas is okay - but "copying" it is not. Her quilt basically uses rectangles to mimic the more difficult double wedding ring pattern. If you want to draft your own rectangles to accomplish that - fine. I suspect other people have done that in the past. You may wind up with something very similar, or even identical to Judy's design. But if you attempt to copy her quilt, that's unethical. You're copying her quilt, not her idea.
OK, that's my interpretation of copyright law. I'm not a lawyer, so I may have it wrong. I do think it is very useful for us to discuss this issue freely in this forum.