Both Ricoh WG-5 GPS and Pentax WG-3 have 16.0 MP resolution sensors but Ricoh WG-5 GPS's sensor is (1/2. ) and Pentax WG-3's sensor is 1/2.3-inch (6.17 x 4.55 mm ).
Since Pentax WG-3'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-5 GPS.
Below you can see the WG-5 GPS and WG-3 sensor size comparison.
As seen above, Pentax WG-3 has a infx Larger sensor area than Ricoh WG-5 GPS. 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.