Both Casio EX-10 and Canon SX40 HS 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 SX40 HS'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 SX40 HS.
Below you can see the EX-10 and SX40 HS sensor size comparison.
As seen above, Casio EX-10 has a 1.5x Larger sensor area than Canon SX40 HS. 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.