Originally Posted by desconhecido

"A double butted spoke is like 3 springs in series. Maybe this is the key difference?"

Yes, that's right, it's like three springs in series. A straight gauge spoke is three springs in series too, it's just that they are all the same. In either case if you apply the same load to the three springs in series, the elongation of the two outer springs is the same -- Hooke's law. If the middle spring is springier, it will elongate more and the total elongation will be more, but the end springs will behave the same.

What we're not considering, and which I don't have the tools to consider or understand, is how the rim behaves when there are butted spokes as opposed to straight gauge spokes. Is the deformation still confined to essentially the same section of the rim or is the deformation significantly more extensive with butted spokes.