what is the difference between the way D3X and H3D-39 derive higher ISO's?
Real ISOs refer to the gain of the amplifier that feeds the captured information from the sensor into the AD converter.
Fake ISOs are shots obtained at a different (usually lower) real ISO value and then overexposed by the camera software.
A camera usually has some real ISOs, and also several fake ISOs. For example on a Canon 5D, ISO3200 is fake ISO. The shot is actually taken at ISO1600 and then overexposed by 1 stop (all levels are multiplied by 2) before saving the RAW data.
A fake ISO like the ISO3200 on the Canon 5D has no noise advantage when shooting RAW over shooting at the same aperture/shutter using the lower real ISO (ISO1600 in the example), because it's actually a ISO1600 shot. But the fake ISO can make us loose up to 1 stop of highlights information because of the overexposure.
So fake ISOs should always be avoided when shooting in RAW mode or we can loose DR in the highlights when comparing to shooting at the same aperture/shutter with the highest real ISO.
In JPEG mode all ISOs are fine, as long they help us to achieve the correct exposure in the final image, since this will be hardly corrected.
Looking at the plot, it seems the Hasselblad has only one real ISO (ISO50). When setting ISO100, 200 or 400 on that camera, the shot will be internally done at ISO50 and then respectively overexposed by 1, 2 or 3 stops in software. So shotting at any ISO over 50 in the Hassy is useless and can make the user loose highlights information with respect to using the same aperture/shutter and ISO50.