Umm, actually, you can increase the quality without increasing the per-pixel size on the CCD. Look to Nikon (CCD) and Canon (CMOS) DSLR evolution in the time that iSight has been out; look to revolutions like the Foveon sensor (which I hear is finally going to be announced in a Sigma DSLR at Photokina). While these are "still" sensors, the same principle applies to digital video sensors (I'm just not as familiar with them, although I'm very happy with my Panasonic 300 camera's quality especially in low light, compared to my old Sony TR80's, which so far as I understand is actually with a smaller sensor and optics).
While at any given point in time, more space on the sensor per pixel will result in a less-noisy image at a given ISO sensitivity, that is certainly not the only way to get a higher-quality picture given technological advances over time.
iSight (the separate component) stagnated a while back, and the world of digital imaging has passed it by. I suspect we could well see a significant increase in image quality and resolution with the same size sensor and optics (although the optics may need refinement to meet the standards of a more modern sensor).