Both Fujifilm A100 and Leica M8 have 10.0 MP resolution sensors but Fujifilm A100's sensor is 1/2.3-inch (6.17 x 4.55 mm ) and Leica M8's sensor is APS-H (27 x 18 mm ).
Since Leica M8'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 A100.
One other difference between these two cameras that is worth mentioning is that Leica M8's sensor doesn't have an anti-alias (Low-Pass) filter. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moiré occurring in certain scenes.
Below you can see the A100 and M8 sensor size comparison.
As seen above, Leica M8 has a 17.3x Larger sensor area than Fujifilm A100. 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.