Both Panasonic ZS3 and Sony A330 have 10.0 MP resolution sensors but Panasonic ZS3's sensor is 1/2.3-inch (6.08 x 4.56 mm ) and Sony A330's sensor is APS-C (23.5 x 15.7 mm ).
Since Sony A330'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 Panasonic ZS3.
Below you can see the ZS3 and A330 sensor size comparison.
Sensor Size and Resolution Comparison image of Panasonic ZS3 and Sony A330 Cameras
As seen above, Sony A330 has a 13.3x Larger sensor area than Panasonic ZS3. 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.