I've heard that advice, and I think it's appalling (although the reasons are understandable). So, professionally published authors are expected to do all the marketing and publicity for their books (via social media, blog tours, giveaways etc), they're meant to use their own money to commission art and merchandise to give away for preorder campaigns, and they're meant to use their own money to have the book professionally edited? At this point, what is the publisher even there for? I agree with you that it starts to make more financial sense to self-publish, although you need to be very good at marketing for that to be a success.