The reason for this change was that it was reported that specular was being incorrectly affected by material opacity - making it difficult to render correct looking shiny translucent materials such as glass. It was also known that material opacity is also sometimes used to fade in or out objects - and when fading in or out objects, it is expected that the specular highlights on shiny objects are also faded in or out.
After some discussion, the solution implemented was to add a flag to prevent specular from being affected by material opacity if set to false, but set the flag default to true so that existing materials in existing projects continue to render as they did before the change. A new material value was added to allow objects to be faded in or out when specular is flagged to not be affected by material opacity.
Once the new material properties are exposed in the editor, it is likely that we will want to set the opacityFadesSpecular flag to false in newly created materials and recommend that if fading objects in or out in scripts, that the alphaFade value is used. For existing projects, if you wish to have un-faded translucent specular, you can set the opacityFadesSpecular to false and if you do fade in or out objects by changing the material opacity value in scripts, you can change the alphaFade value instead.
Hopefully this answer helps to clarify what was changed and why.