Welcome to the world of posting on HN! I think the either/or mentality is entirely rooted in billing; you either pay CPC/CPA (Cost Per Click / Cost Per Action)

Welcome to the world of posting on HN! I think the either/or mentality is entirely rooted in billing; you either pay CPC/CPA (Cost Per Click / Cost Per Action), or you pay CPM (cost per 1K impressions), but not both. The interesting question is, why not charge for both?