Both Casio EX-10 and Canon SD940 IS have 12.0 MP resolution sensors but Casio EX-10's sensor is 1/1.7-inch (7.44 x 5.58 mm ) and Canon SD940 IS's sensor is 1/2.3-inch (6.17 x 4.55 mm ).
Since Casio EX-10'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 SD940 IS.
Below you can see the EX-10 and SD940 IS sensor size comparison.
As seen above, Casio EX-10 has a 1.5x Larger sensor area than Canon SD940 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.