Yes it should be a "+", thank you.
Just because marginal cost for software can be close to zero in some circumstances does not make demand curves meaningless!
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!