“This view shows just how different the economic value of users can be. In the case of Apple, it’s growing its user base at (literally) exponential rates. The revenues per user does, understandably, decline. This is because new/later users don’t spend as much as early users. There might be some stability toward the later stages of adoption in revenue per user. The other point about iTunes data is how the mix of revenues has shifted from music to Apps and Services pointing out how users can be migrated across revenue sources over time.
In the case of Amazon it’s growing its user base at a linear rate (note equation). The revenue per account remains very steady however.”