Why does it subtract the marginal cost? According to the formula the more it costs to make the product (per customer/sale cost) the cheaper you should sell it.
B basically any economic reasoning around “demand curve” and “marginal cost” is meaningless in real world situations.
Just because marginal cost for software can be close to zero in some circumstances does not make demand curves meaningless!
The so-called demand curve is as useful for a business as a population-wide heartbeat distribution would be. It makes no sense to talk about “the” curve, since it changes all the time!