Both Nikon D80 and Sony H20 have 10.0 MP resolution sensors but Nikon D80's sensor is APS-C (23.6 x 15.8 mm ) and Sony H20's sensor is 1/2.3-inch (6.17 x 4.55 mm ).
Since Nikon D80's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Sony H20.
Below you can see the D80 and H20 sensor size comparison.
As seen above, Nikon D80 has a 13.3x Larger sensor area than Sony H20. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.