Why is D90 betten then D300s at DxOMark Sensor test?
Because D90 have some 'tweaks' to punch the color values from sensor of D90.
It costs more saturation and more color errors. That not acceptable for 'pro' D300-D300s.
Another is more smooth and less acute picture due to weaker moire filter before the sensor, i.e. less resolution and less microcontrast in D90. That masks much of noise in sensor tests.
Just look at non linear curves on DXOmark for D90
DxOMark tests RAW data - uncooked RAW data, so your words doesn't apply.
I wonder why Nikon D90 got a better rating (72.6) then Nikon D300s (69.8) at the http://www.dxomark.com/
Nikon D300s is newer and more expensive.
Can any one explain that?
Best regards from Denmark...
That is 1/6 of a stop difference, and most likely are in their margin of error.
EDIT: I mean 1/5 of a stop difference. (15 points equals to one stop)