Some advertisers offer multi-tier programs that distribute commission into a hierarchical referral network of sign-ups and sub-partners. In practical terms: publisher "A" signs up to the program with an advertiser and gets rewarded for the agreed activity conducted by a referred visitor. If publisher "A" attracts other publishers ("B", "C", etc.) to sign up for the same program using her sign-up code all future activities by the joining publishers "B" and "C" will result in additional, lower commission for publisher "A".
Snowballing, this system rewards a chain of hierarchical publishers who may or may not know of each others' existence, yet generate income for the higher level signup. This sort of structure has been successfully implemented by a company called Quixtar.com, a division of Alticor, the parent company of Amway. Quixtar has implemented a network marketing structure to implement its marketing program for major corporations such as Barnes & Noble, Office Depot, Sony Music and hundreds more.
Two-tier programs exist in the minority of affiliate programs; most are simply one-tier. Referral programs beyond 2-tier are multi-level marketing (MLM) or network marketing.
Even though Quixtar compensation plan is network marketing & wouldn't be considered 'affiliate marketing', the big company partners are considered and call themselves affiliates. Therefore, you may argue that the Quixtar company is the affiliate marketer for its partner corporation.