In ANZO, when the IAS memberships first came in, they weren't mandatory if one wanted to receive services. Very soon afterward they became mandatory, and one wasn't permitted to receive services without a current membership. The "discount" remained in place - just a farce.This list is of the higher level contributors. It starts out with the level of a free 6 month Intro membersip. Then there are annual and lifetime members.
Maybe someone will know a reference, but when I was on staff you would have to be an IAS member to be in the HGC or Academy, and there was something written that was shown. There was a huge panic trying to get money together for my son's annual membership once because his lapsed during a week he was being put on the grid to comp. So, those discounts are pointless and perhaps 'proof' to outsiders (who don't see behind the scenes) that membership is voluntary. More smoke & mirrors.