I would suspect lots of Hollywood Accounting is likely; putting all the PostOpen software in a subsidiary that has no revenue, or developing your own software under PostOpen but not distributing it outside, so that the majority of the usage is apportioned to affiliated companies.
Plus, apportioning by usage is a negative incentive for optimization. If your DB reduces query runtime by 10% in the next version, it reduces its revenue, assuming other PostOpen software is in use and doesn't optimize.