tuco, I bow to your knowledge of B&W photography.
Actually, I think you are a talented photographer in color too. As are many Nikon users, as evidenced by the various threads around this forum.
I'm not sure my red filter analogy makes sense. After all, I have very limited experience with B&W + filters.
My point wasn't so much about B&W filter use. I'm certainly not an authority on that subject (or other subjects, but hey: Internet).
My point was really that the different manufacturers have different sensitivity curves for the different color channels, and the curve for Canon's red channel includes more influence outside of the red part of the spectrum. Therefore, the presence of blue or particularly green light will appear as red from the Canon sensor. I believe that this tends to smooth out skintones.
For example, the chart for spectral sensitivity shows that Canon has a 20% relative sensitivity to 550 nm light (green), whereas Nikon has essentially 0% sensitivity at that wavelength. So green light will contribute to Canon's red.
I don't think this is a "mistake" or some failure by Canon to develop a better color filter. I think that Canon image scientists tune their sensor to have this property because they've found that some portion of people prefer the look.
And I think that this is only one example of the type of difference that can be measured. Who knows what kind of tricks are baked into the RAW files, or even baked into Lightroom's RAW converter?