SquareScale pricing model is thought both to ensure you pay only what you use and to be as simple to understand as possible.
In addition to the fixed costs like base infrastructure, SquareScale also charges you some variable fees. We do it because we rely on AWS and they compute their price reflecting traffic load and storage use.
We could definitely have hidden the variable fees to our customers. Indeed, these costs are meaningless in most cases. But for customers with irregular peaks in load or a lot of traffic, these can be significant.
By removing the variable fees, we would have had to increase the fixed price of the cluster elements to take into account the average variable fees of all customers. It would have been unfair for customers with low traffic and wouldn't be consistent with our "pay as you go" principle.
In order to keep the "pay as you go" principle, and to avoid the complexity of the AWS price computation, we have simply described different scnenarios on our pricing page to give customers some concrete examples.