No sorry thats not the physics at all.

Better fabrication process = better sensors = better images, photodiodes need to be made more identical to all the others on the same sensor, the more identical they are, the less noise they produce, as they'll produce more identical results, smaller photodiodes need to be even more indentical to maintain same noise levels of larger sensors, which is harder to do, as CPU tech increases and uses smaller fabrication processes, so will CMOS sensors, they can be smaller, or higher resolution or both (ie: smaller photodiodes), CMOS is the same process used for CPUs.
http://en.wikipedia.org/wiki/CMOS
http://en.wikipedia.org/wiki/Active_pixel_sensor

You're comparing a mass produced small sensors from consumer plants, versus expensive professional sensors, they're bigger and more expensive, and more refined in their R&D process, smaller photodiodes are much more difficult to process, and they have less R&D and are much cheaper cameras, and using a cheaper fabrication process. duh.

smaller photodiodes are more sensitive than larger ones, if a photodiode is 1/4th the size of one in another sensor, it is 4 times more sensitive, if they both receive 10,000 photos, the smaller one is more sensitive, it in reality it'll only receive 25,000 as its area is only a quarter of the larger, thus produces the same sensitivity levels, it needs have a more refined fabrication process, the CMOS process is exactly the same, in fact it IS the process for fabrication of CPUs, making smaller photodiodes is more difficult and they need to be made more identical to the ones around them to keep noise down (same with the second photo resistor).