Casio EX-10 has a 12.0MP 1/1.7" (7.44 x 5.58 mm ) sized CMOS sensor and features Exilim Engine HS 3 processor. On the other hand, Olympus E-PM2 has a 16.0MP Four Thirds (17.3 x 13 mm ) sized CMOS sensor .
Below you can see the EX-10 and E-PM2 sensor size comparison.
As seen above, Olympus E-PM2 has a 5.4x Larger sensor area than Casio EX-10. 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.