@ggbutcher
Glenn, I think it is not astonishing that the response curves for Nikon cameras are very similar. They all, most likely, use the same filter technique, the same sensor technique, resulting in the same response curves. Lenses also play a role but I would assume, that is a minor issue. Otherwise changing the lens would ruin the colours…
As Hunt (2004) shows, the spectral sensitivity curves of digital cameras are matrixed to approximate the colour matching functions as close as possible. But how exactly, that certainly differs from manufacturer to manufacturer. He also cites work on the spectral sensitivities of digital cameras (Hubel, Sherman and Farrell, 1994).
Hermann-Josef