Both Ricoh GXR S10 24-72mm and Ricoh GXR P10 28-300mm have 10.0 MP resolution sensors but Ricoh GXR S10 24-72mm's sensor is 1/1.7-inch (7.44 x 5.58 mm ) and Ricoh GXR P10 28-300mm's sensor is 1/2.3-inch (6.17 x 4.55 mm ).
Since Ricoh GXR S10 24-72mm'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 GXR P10 28-300mm.
Below you can see the GXR S10 24-72mm F2.5-4.4 VC and GXR P10 28-300mm F3.5-5.6 VC sensor size comparison.
As seen above, Ricoh GXR S10 24-72mm has a 1.5x Larger sensor area than Ricoh GXR P10 28-300mm. 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.