RV, you're drawing the wrong conclusion.

Uwe said without diffuse the whole chain would not react to light. Then you suddenly and without any justification equated that to multiplication.

It's nothing of the kind. The color ramp has four colors in it. The Diffuse node drives the lookup of one of those colors. When diffuse is black, or 0, then the first color is chosen. When the diffuse is pure white, or 1, then the last color is chosen. When diffuse is 1/3, the second color is chosen. When diffuse is 2/3, the third color is chosen. Other values select blended versions of the two closest lookup values. 

This technique was published by me in 2006 as a way to add some red to the skin in the shadowed areas. This was the earliest SSS faking tactic that I published as a way to avoid having to use/run face_off's realskin shader over and over. His technique for adding red was based on a script examining the location of the light. My technique was to have the shader do that. How does a shader examine the location of a light? It can't - not really. Not with the nodes Poser gives. But this hack worked in a lot of cases using the Diffuse node as proxy to answer the question "am I pointing away from the light". In low light, or very bright ambient light, it gives the wrong answer.  But in typical Poser-style portrait lighting, it gives the right answer.

When Daz hired face_off to produce the V4 shader, he decided to use this trick in the official V4 shader. Subsequently, almost every vendor copied this style, even though published better tactics in VSS and kept improving the trick in PR2 and PR3. As of PR4, it's quite sophisticated and is able to reproduce front-side scatter almost as well as the new scatter node in P9/2012.

The worst thing about the Diffuse->ColorRamp in the way people use it is it doesn't work right/same when render GC is enabled.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)