If Netflix is saving a shit-ton of money and providing a better service to their customers by peering, and Comcast has less upside, why shouldn't Comcast charge Netflix for the privilege?
I don't know if we can accurately estimate who's saving how much, and I definitely don't believe anything coming from Comcast. Given that there is no way to reach Comcast customers other than Comcast and both parties have an incentive to lie about their costs, I think zero is the fairest price for such peering.