This model is different from a subscription in that: It covers the cost of publishing content not reading content.  It transparently links fees and tiers. Historically subscription models have never been fully transparent about what constitutes the basis for their fees.  The margin is capped because the goal is sustainable selective publishing – NOT revenue maximization.  Revenues return to community members at renewal if/when the group achieves the revenue target. PLOS does not keep additional revenue above the target.