Both Casio EX-100 and Canon SX200 IS have 12.0 MP resolution sensors but Casio EX-100's sensor is 1/1.7-inch (7.44 x 5.58 mm ) and Canon SX200 IS's sensor is 1/2.3-inch (6.17 x 4.55 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 Canon SX200 IS.
Below you can see the EX-100 and SX200 IS sensor size comparison.
As seen above, Casio EX-100 has a 1.5x Larger sensor area than Canon SX200 IS. 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.