When you double the quantity of a curry recipe you don't double everything in it. The spices and other ingredients are only increased by 50% with the exception of the main ingredients like the meat / vegetables.
As Phil and curryhell have pointed out, we don't always agree. Part of the reason might be that I don't think there's a single high-calibre, formerly qualified professional chef amongst us. That means we're a bunch of well-intentioned amateurs.
My take on quantities, is that Livo's advice is wrong, wrong, wrong! It makes no scientific sense at all.