Both Ricoh GXR S10 24-72mm and Nikon 1 J2 have 10.0 MP resolution sensors but Ricoh GXR S10 24-72mm's sensor is 1/1.7-inch (7.44 x 5.58 mm ) and Nikon 1 J2's sensor is 1-inch (13.2 x 8.8 mm ).
Since Nikon 1 J2'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 Ricoh GXR S10 24-72mm.
Below you can see the GXR S10 24-72mm F2.5-4.4 VC and 1 J2 sensor size comparison.
As seen above, Nikon 1 J2 has a 2.8x Larger sensor area than Ricoh GXR S10 24-72mm. 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.