I feel like there is some misunderstanding here. What is publishers' profits, where do they come from? Publishers don't deposit anything, it is advertisers' money anyway.
We know our fee is high, but it is not 40%. As I said, it is 10-36% depending on the particular use case.
We take a deposit fee of 20%, half of it is a reward for publisher that attracted advertiser.
Then we distribute remaining 80% to ad units that satisfy advertiser's criteria (with respect to Daily Budget set by advertiser) and take 20% fee from it. In return advertiser receives proportional share of impressions of those ad units.
But advertiser can set Daily Budget to 0 and spend campaign's balance via Goal Tracking API without that 20% fee.
So the principle is simple: money gets distributed from advertisers to publishers (either we distribute it according to some simple internal algorithm for a 20% fee, or advertisers distribute them via Goal Tracking API without a fee). In return advertisers get proportional share of impressions from ad units they pay to. No absolute numbers of clicks/impressions are guaranteed though, CPC and CPI are just rough estimates.
Also if advertiser is at the same time a publisher, then instead of depositing money s/he can redirect his earnings to campaign with only a 10% fee.
Thus minimum fees we take from advertiser is 10%, maximum is 36% and our fee model encourages advertisers to reward ad units that work best for them thus minimizing incentive for fake traffic. But we might consider to change it.
Thanks for your feedback!