As the process size gets smaller, power usage decreases.
Smaller transistor processes allow the use of lower voltages combined with the improvements in construction technique mean that a ~45nm processor can use less than half the power that a 90nm processor uses with similar transistor counts.
The reason for this is that as the transistor gate gets smaller, threshold voltage and gate capacitance (required drive current) gets lower.
It should be noted that as Olin pointed out this level of improvement doesn't continue to smaller process sizes as leakage current becomes very important.
One of your other points, the speed at which signals can travel around the chip:
At 3ghz the wavelength is 10cm, however the 1/10th wavelength is 1cm which is where you need to start considering transmission line effects for digital signals. Additionally remember that in the case of Intel processors some parts of the chip runs at twice the clock speed so 0.5cm becomes the important distance for transmission line effects. NOTE: they may be operating on both clock edges in this case, meaning the clock doesn't run at 6Ghz but some processes going on are moving data that fast and have to consider the effects.
Outside transmission line effects, you also have to consider clock synchronization. I don't actually know what the propagation velocity is inside a microprocessor, for unshielded copper wire its like 95% of the speed of light but for coax is like 60% the speed of light.
At 6Ghz the clock period is only 167 picoseconds the so high/low time is ~ 84 picoseconds. In vacuum, light can travel 1cm in 33.3 picosends. If the propagation velocity was 50% the speed of light then its more like 66.6 picoseconds to travel 1 cm. This combined with the propagation delays of the transistors and possibly other components means that the time the signal takes to move around even a small die at 3-6Ghz is significant for maintaining proper clock synchronization.