Why only Sig for Scale Cubs?
You must also realize that in this hobby, there is "Scale" and "Stand Off Scale".
A "Scale" kit is built to the exact dimentions, using the same building techniques. That is to say, that if the Full Scale plane has 24 ribs, the Scale plane will also have 24 ribs Etc,etc,etc.
A "Stand Off Scale" plane will look like it's Full Scale counterpart from a small distance, but upon close examination, you will see that it may have only 20 ribs (along with many other differences).
The reason being that the smaller version doesn't NEED all of the same things as the Full Scale version. And while the designers are at it, they may also determine that a different airfoil, or different wingspan would suit a smaller plane better.
So they design a plane that will be an easy-to-build, great flying "Model" of a Full Scale Cub.