Peering is about "equal value". Consider the pure content provider co-located witht he pure eyeball provider, where neither have a long haul network (eg local providers, similar bit/mile cost on each side). The costs are equally distributed, both get similar "value" from the interconnection (and indeed, can't exist without each other in the pure case), but the ratio may well be 10:1.

Nobody has mentioned a key step. How do you decide what the value is to each player? I assume everybody here expects the free market to make that decision. I see no reason to assume that each side of a connection is getting an equal value just because traffic is ballanced or the conditions meet somebody's peering checklist. Letting the market make that decision gets complicated if one of the players is a 900 pound gorilla. Note for example, that the price of old newspaper changes from positive to negative as market conditions fluctuate. If something is scarce, it's valuable scrap and people will pay you for it. If there is too much, it's trash and you will have to pay somebody to haul it away. The guy who runs the trucks may be a broker too, trying to make a buck any way he can. I could easily imagine that the price of eyeballs and content would fluctuate in a similar way - or that a backbone would could play broker.