Both Sony A100 and FujiFilm F70EXR have 10.0 MP resolution sensors but Sony A100's sensor is APS-C (23.6 x 15.8 mm ) and FujiFilm F70EXR's sensor is 1/2-inch (6.4 x 4.8 mm ).
Since Sony A100'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 FujiFilm F70EXR.
Below you can see the A100 and F70EXR sensor size comparison.
As seen above, Sony A100 has a 12.1x Larger sensor area than FujiFilm F70EXR. 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.