A $500 APS-C DSLR can use the exact same sensor and DSP as a $2000 APS-C DSLR and yet people still buy the $2000 version because of the features and capabilities.
...Also, two cameras that use the identical sensor are not guaranteed to produce the same image. The electronics package in each camera and how it processes the sensor image can radically change the finished result. So often you are paying for a lot more than just the sensor with the higher priced camera.