Somewhere I still have spectral curves on file for Pentax and related Minolta spot SPD meters. It's a symmetrical bell curve distinctly topping at 550nm green. Since these meters were, and still are, targeted to not only still photographers, but cinema and TV applications, it was important to publish the sensitivity curve, especially in comparison to older CDS meters which had different sensitivity. Via testing, I figured out that the SPD sensor in my Nikon FM2n has essentially the same characteristics as the other SPD's.
Ice-Racer - I don't see how this is necessarily related to some ancient comparison article at all, imagining some kind of unrealistic compromise between between daylight and tungsten sources. Kelvin is kelvin. And if you want a deliberately skewed reading for a particular light balance, there is a filter thread on some of these spotmeters as well.
Brian - therefore SPD readings aren't wonky at all. They're ideal in the sense that they correspond to peak human visual sensitivity itself, right in the middle of the visible spectrum. And yes, the given distinctions are quite significant in real world photography. You need to know, or at least be accustomed to, your own meter's specific personality, with its own spectral sensitivity.
Mark - those Zone VI conversions were calibrated to Tri-X Pan 320 film. Not all pan films are the same in terms of actual spectral sensitivity, and then you've got entirely different films too - othopan, ortho, and blue sensitive, plus different kinds of color film. And the conversion filter installed in those modified units fade anyway over time. The pros and cons can be looked up elsewhere.
Manufacturers of digital cameras no doubt have their own results tucked away somewhere, or otherwise obvious to engineers. The lack of that up front for consumers is probably just a marketing choice. But who knows? ... maybe its in subsection 392.5a.1 on p. 792 of the owner's manual, after you've already read through the first 791 pages just trying to learn how to turn off all the silly apps in order to take a basic picture.