Its the one thing I agree with DxOMark about.
All the cameras have different results when you put the ISO to 100, put them same lens on all of them and shoot the same picture with the same shutter speed and aperture. This can only be to the misrepresentation of the actual speed of the sensor.
Its crap, because we all know that ISO is a standard, but its just a way for the marketers to market their 6400 ISO and other crap.
There is nothing you can do about it but compensate. Unfortunate