Ricoh GXR S10 24-72mm F2.5-4.4 VC has a 10.0MP 1/1.7" (7.44 x 5.58 mm ) sized CCD sensor and features Smooth Imaging Engine IV processor. On the other hand, Nikon D5100 has a 16.0MP APS-C (23.6 x 15.7 mm ) sized CMOS sensor and features Expeed 2 processor. Nikon D5100's sensor provides 6MP more than Ricoh GXR S10 24-72mm F2.5-4.4 VC'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 GXR S10 24-72mm F2.5-4.4 VC and D5100 sensor size comparison.
As seen above, Nikon D5100 has a 8.9x Larger sensor area than Ricoh GXR S10 24-72mm F2.5-4.4 VC. 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.