I am not a business guy and don't need to understand what their model is. I understand my model - that I test network software and I don't want to trudge through amazon lookups in wireshark.
you -> developer
then the developer is only interested in making you happy, because you're the payer. However, if the relationship is like this: you -> advertising company -> developer
then the developer doesn't really care about you; you're just the means to an end, a vehicle to drive to the place with money. The developer and advertiser will build a business relationship, <cynical> and usually make sure their relationship with you maximizes shareholder (not your) value. </cynical>