Ricoh WG-6 has a 20.0MP 1/2.3 (6.17 x 4.55 mm ) sized BSI-CMOS sensor . On the other hand, Olympus FE-4000 has a 12.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor and features TruePic III processor.
Ricoh WG-6's sensor provides 8MP more than Olympus FE-4000's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
Below you can see the WG-6 and FE-4000 sensor size comparison.
Sensor Size and Resolution Comparison image of Ricoh WG-6 and Olympus FE-4000 Cameras
Ricoh WG-6 and Olympus FE-4000 have the same sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture. On the other hand, since Olympus FE-4000 has 71% larger pixel area (2.38µm2 vs 1.39µm2) compared to Ricoh WG-6, it has larger pixel area to collect light hence potential to have less noise in low light / High ISO images.