Both Olympus FE-5010 and Olympus E-P1 have 12.0 MP resolution sensors but Olympus FE-5010's sensor is 1/2.3-inch (6.08 x 4.56 mm ) and Olympus E-P1's sensor is Four Thirds (17.3 x 13 mm ).
Since Olympus E-P1'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 Olympus FE-5010.
Below you can see the FE-5010 and E-P1 sensor size comparison.
As seen above, Olympus E-P1 has a 8.1x Larger sensor area than Olympus FE-5010. 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.