There appears to be a bug impacting the “Added lightning damage with Shurikens” affixes. I rolled a new rogue to do some baseline testing and noticed some peculiar results:
Equipping a chest, helm (or both) with the added lightning damage affix did not change the damage of shurikens at all (both observed and tooltip DPS). Affix had NO EFFECT on damage but skill visualization changed and lightning tag was added.
Equipping a ring with +physical damage to throwing did make noticeable difference, no issues here.
I specced into Shuriken to test with the skill point node that adds lightning damage and there is an interaction here that I am not sure is intended. The talent does add base damage to the skill appropriately AND once the talent is specced, the added lightning damage with shurikens affixes now DO apply their additional damage.
Basically, my testing indicates the affix only applies if you have already taken at least one skill point in the skill tree node. Is it intended for this skill node to gate the affix effect? It did not seem clear to me that was how the affix would work and the relative value of the affix makes the skill node less attractive (unless you know you need it for the affix to work!)