It's a cap. It's not a statement of how _much_ you can charge, just what the maximum charge can be. How much you actually charge can be based on the things you

It's a cap. It's not a statement of how _much_ you can charge, just what the maximum charge can be. How much you actually charge can be based on the things you mention, but you can't charge any more than that 10%. Also, a maximum %age is easier to regulate, while the factors you mention are significantly harder to regulate. Moreover, %ages don't need readjusting to account for inflation.