Both Nikon D2Xs and Samsung HZ25W have 12.0 MP resolution sensors but Nikon D2Xs's sensor is APS-C (23.7 x 15.7 mm ) and Samsung HZ25W's sensor is 1/2.3-inch (6.08 x 4.56 mm ).
Since Nikon D2Xs'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 Samsung HZ25W.
Below you can see the D2Xs and HZ25W sensor size comparison.
As seen above, Nikon D2Xs has a 13.4x Larger sensor area than Samsung HZ25W. 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.