Both Pentax WG-2 GPS and Ricoh WG-80 have 16.0 MP resolution sensors but Pentax WG-2 GPS's sensor is 1/2.3-inch (6.17 x 4.55 mm ) and Ricoh WG-80's sensor is (1/2. ).
Since Pentax WG-2 GPS'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 WG-80.
Below you can see the WG-2 GPS and WG-80 sensor size comparison.
As seen above, Pentax WG-2 GPS has a infx Larger sensor area than Ricoh WG-80. 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.