Both Panasonic LX3 and Ricoh GR Digital III have 10.0 MP resolution sensors but Panasonic LX3's sensor is 1/1.63-inch (8.07 x 5.56 mm ) and Ricoh GR Digital III's sensor is 1/1.7-inch (7.44 x 5.58 mm ).
Since Panasonic LX3'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 Ricoh GR Digital III.
Below you can see the LX3 and GR Digital III sensor size comparison.
Panasonic LX3 and Ricoh GR Digital III have almost the same sensor size, so neither of them has any significant advantage over the other in terms of providing control over depth of field when used with the same focal length and aperture.