Quick and dirty translation of this; feel free to make corrections as I know nothing about the actual innards of the PS3:
Heatsink shaved in line with the fan. To save on surface area, fins are made wave-shaped.
In the CECH-2500, the fan is right above the RSX heat spreader, so we used a heat pipe to move the RSX heatsink's position to a place where it wouldn't interfere with the fan. But with the CECH-3000, the fan itself has become smaller, so we no longer had to move it and could eliminate the heat pipe entirely, making the heatsink bigger.
About 220 grams were saved with the two metal shields surrounding the main board, the heatsink, and the fan motor. The BD drive went from 458 grams to 404, becoming about 50 g lighter, and [adding together the reductions in] other parts (board, power/eject buttons, etc.) made the machine 400 g lighter in total. The power supply unit itself remains unchanged.
While power consumption, parts, and the Cell/RSX(?) have shrunk, there are no significant changes in the circuitry. The new design thus creates a model that further reduces costs.