Just wondering whether the top earners are getting bonuses or additional payouts from their merchants for bringing in so much business?
Not on Clickbank, but on other networks, sure. CB is just a part of my business, I'm with MarketLeverage and myHelpHub too, among others.
It depends, if you are able to contact the merchant you may be able to get bonuses and some people run competitions every month for their affiliates (even here on this forum).
I get a $500/month bonus with one merchant as long as I stay above 500 sales/month. Other merchants offer a bonus for everyone. One of the accounts I promote actually pays 100% commission. They pay the non-clickbank portion through paypal every 2 weeks.