Mick, I offer these comments as an engineer with a few years practice at looking at broken bits. Of course I'm not privy to your dealings with Galpro, so these points may have already been raised and discussed. Apologies if that is the case. Also trying to reach conclusions from a few photos is also a little tricky .
Anyhow. *The original threads were most likely rolled which does make a stronger component as opposed to the cut threads, however the better grade of material may compensate for this.
* The smaller diameter convex section is usually around the root diameter of the thread which gives a better distribution of stress in the bolt. The detail around the termination of the cut thread is important to ensure minimal stress concentrations.
* My 100 (and I'm sure other
wheels are the same) has split rims, the centre of the rim fits snugly over the hub therefore the centralising and weight bearing is taken care of. I could not see that detail in your photos. The studs shouldn't be taking weight etc, just supply clamping force.
* The above comment is based on the photo of the broken studs. To me they appear to have a fatigue failure (as opposed to shear), something that could come from taking the weight from a rim centre diameter problem and then subject to cyclic, bending loads.
However, all that said, I will be having a very close look at my studs before the next trip. Thanks for your story.