[tpmoney]

On the gripping hand:

They already do take that tithing, in the form of the amortized cost of the car over those transactions. Admittedly the amortized cost of your car doesn't scale with your transaction volume or income (baring extra wear and tear concerns) but – as long as we're torturing analogies to death – you also can't buy your car on a "no up front costs and no costs at all to try it out for yourself and a flat $100 / year as long as you don't make money with your car and 15% on revenue if you do" lease agreement.