Of course not. Paying for bandwidth asymmetry is only used where its logic makes sense. The basic underlying assumption is that traffic that begins on one network and terminates on the other benefits both sides equally and thus the costs should be split roughly evenly. Paying for bandwidth asymmetry is an approximation to cover the case where one side pays more than the other, usually because one side has to carry the traffic further than the other. (Generally, you carry inbound traffic further than outbound.) Historically, this is the way it's done.

But when you're talking about Comcast, which has a large number of small endpoints, and Netflix or Crashplan, which have a small number of large endpoints, more of the costs are borne by Comcast regardless of the direction. So settlement-based peering makes sense regardless of traffic ratios.

Settlement-based peering based on traffic ratios makes sense when you're talking about two ISPs with roughly similar business models, types of customers, and service areas. But it's just a simple approximation of the underlying logic -- traffic benefits the sender and receiver about equally, so they should split the costs about equally. When design asymmetries make one party pay more than their fair share, settlement-based peering is the norm.