Both Nikon S630 and Casio EX-100 have 12.0 MP resolution sensors but Nikon S630's sensor is 1/2.3-inch (6.08 x 4.56 mm ) and Casio EX-100's sensor is 1/1.7-inch (7.44 x 5.58 mm ).
Since Casio EX-100'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 Nikon S630.
Below you can see the S630 and EX-100 sensor size comparison.
As seen above, Casio EX-100 has a 1.5x Larger sensor area than Nikon S630. 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.