To put it as simply as possible, if the articles do in fact mean to claim that Athlons now use the 12V rail for power, they are largely looking at atypical examples and towards the future, speculating this will happen. Of course some Athlon motherboard(s) DO use 12V, but they are still a minority. Only time will tell, there is currently no technical need to move to 12V, the greater problem is heat radiation, to use more current than contemporary 5V designs can provide, they need better cooling than air can provide.
Some nForce2 boards do, like the nVidia reference design and MSI nForce2, but then some Asus don't.
nForce1, most KT400, KT333, KT266, etc, boards usually do not use 12V for the CPU (seems Abit does more often use 12V, MSI does on occasion but not most of the time, same with Gigabyte's newer boards).
Certainly it's true that for a power supply to be viable in the future, it needs a large 12V capacity for use with P4, lots of HDD, or those certain boards that do use 12V for the CPU.
On the other hand, I have a motherboard that used 12V for an o'c Athlon XP, with 3 HDD and typical fan setup, all on a non-ATX12V PSU (a ATX12V plug adapter was used) rated at 13.5A on the 12V rail IIRC (the Delta 300W PSU deal from Directron a few months back).