Both Panasonic LX10 and Sigma DP2 Quattro have 20.0 MP resolution sensors but Panasonic LX10's sensor is 1″ (13.2 x 8.8 mm ) and Sigma DP2 Quattro's sensor is APS-C (23.5 x 15.7 mm ).
Since Sigma DP2 Quattro'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 LX10.
Below you can see the LX10 and DP2 Quattro sensor size comparison.
As seen above, Sigma DP2 Quattro has a 3.2x Larger sensor area than Panasonic LX10. 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.