Both Nikon P7000 and Canon SD4000 IS have 10.0 MP resolution sensors but Nikon P7000's sensor is 1/1.7-inch (7.44 x 5.58 mm ) and Canon SD4000 IS's sensor is 1/2.3-inch (6.17 x 4.55 mm ).
Since Nikon P7000'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 Canon SD4000 IS.
Below you can see the P7000 and SD4000 IS sensor size comparison.
As seen above, Nikon P7000 has a 1.5x Larger sensor area than Canon SD4000 IS. 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.