When I bought FastRaw it was to review and sort photos for keepers. At the time I thought everyone did their histograms the same way.
In fact, I asked on the micro 4/3 forum why the histotrams looked different between the viewer and darktable and got lots of explanations about settings. Nobody that replied talked about the difference between a jpeg histogram and a raw histogram. I believe that the default for Darktable was to use jpegs not raw. Kind of odd given how technical a product it is.
Now that I know how in camera histograms are produced, I can take a series of images at different exposure compensation levels to figure out how I should interpret the in camera histograms for best exposure.
If I were to guess why manufacturers continue to use the jpeg histogram it might be because a majority of people use jpeg rather than processing raw. It seems useful to have a jpeg histogram that shows the result of the in camera processing that creates your image so that you can adjust for 'optimal' jpeg exposure.