Both Casio EX-10 and Sony T90 have 12.0 MP resolution sensors but Casio EX-10's sensor is 1/1.7-inch (7.44 x 5.58 mm ) and Sony T90'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 Sony T90.
Below you can see the EX-10 and T90 sensor size comparison.
As seen above, Casio EX-10 has a 1.5x Larger sensor area than Sony T90. 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.