Why multipple rails instead of a huge one?

Hi!
First of all, please have a look here:
http://www.planet3dnow.de/vbulletin/showthread.php?t=366647&g...

It is a report about the general functions of a ATX Switching PSU.
You can see different pictures about the +12V distribution.
Even one example is to split up the +12V lines and later put them again together in order to show only one line on the safety sticker.

So, as you also can see, mainly they use several lines (even if only one is showed, it maybe also use several ones).
That´s because it is easier to control for the safety functions.
To split up the lines allows you to set a limit per line. Also Intel set some rules in the ATX-specifications 2.X.
Because of the new CPU´s and GPU´s the +12V line was becoming more and more important. Today we know it is the main important line.
Intel wants to split up the lines in order to be sure that there is enough power for their CPU´s.
For example +12V1 with 15A and +12V2 with 8A, but combined only 19A (228W). This is just an example.
So, +12V1 is reserved for CPU and MB (don´t forget the PCI-E Slot, which also needs up to 75W). 12V2 is for periphals like GPU.
So the +12V2 can not exceed the 8A, so at least 11A (from combined power) is left for CPU and MB.
Today this changed because the GPU´s need more power than the CPU (in a good gaming PC). But in general this concept is kept to split up for the different components.

i am kinda guessing here... but since in a modern computer today u have several components that actually use a 12v rail... like 1 or more gpu´s and such... the thing about all electronic equipment is that they dont use a set amount of power *current* instead they only use whats needed for the moment... this would make it very hard to try and make a single 12v capable of handling all the fluxuation that would happen when every different component use more or less current... that and i should think that heat is a big issue... making a single 12v rail would require that it would be able to handle a huge amount of current wich would in turn produce a huge amount of heat!

*edit* ah.. the master got here while i was typing *edit*