Both Canon SX30 IS and Canon G1 X have 14.0 MP resolution sensors but Canon SX30 IS's sensor is 1/2.3" (6.17 x 4.55 mm ) and Canon G1 X's sensor is 1.5 (18.7 x 14 mm ).
Since Canon G1 X'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 SX30 IS.
Below you can see the SX30 IS and G1 X sensor size comparison.
As seen above, Canon G1 X has a 9.3x Larger sensor area than Canon SX30 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.