I didn't have a hand in the discounts code directly but I believe the private API was added last fall so that we could offer this free app to solve most people's needs with discounts ( http://www.shopify.ca/blog/6668676-new-free-shopify-app-bulk... ).

BTW, if you're interested, http://www.shopify.com/careers - things like "I reverse engineered your private APIs and got it on front page of HN" set you apart from the herd ;)