Why is it preferred to transport lower current and higher voltages across the PCB?
There's a limit to how low a resistance you can get on pcb power traces. This has two effects. If you put the regulator far from the CPU, you'll get voltage losses on the PCB, due to the effect of current times resistance. More important, there's no way to compensate for these losses, so the regulation of the voltage at the CPU will suffer.

EDIT For example, let's say that, with the regulator on the other side of the board, the trace resistance is .02 ohms, while with the regulator close to the CPU, the trace resistance is .005 ohms. Furthermore, let's say that the CPU current varies between 5 and 20 amps. Then







simulate this circuit &ndash; Schematic created using CircuitLab

shows how the CPU voltage will vary for the two cases. These numbers are not outrageously out of range, and while a variation of .1 volts at the CPU is not a problem, a variation of .4 volts (on 1 volt) is.

As an example, a Pentium E6300 uses a .85 to 1.375 main voltage, with a power dissipation as high as 65 watts, so the peak current might be in the range of 50 amps.