"Wouldn't then SP rewards be and income/revenue that you immediately reinvest?"

You can only make an investment if you have something to invest with. If there is 13 weeks then you dont have access to fund to invest.

Steemreports financial section is helpful but it is also nice to know where the values came from and how they should be used in accounting. And I am not sure it is fully correct, as for mine it shows power downs, I have never powered down