Today is considered normal to use powers of 1000 instead of 1024(SI x base2) on disks capacity(hd, ssh, usb...), even with our operating systems using base2 measures(except Snow Leopard). This makes our brand new "500GB" HD's actually have 465.66 GB on Linux or Windows.
My question is. I know that this is a common practice but, is there any legal statement, IT standard or historical reason to define SI as the storage measurement by the manufacturers? Or it is just business?